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Is America coming apart? Socioeconomic segregation in neighborhoods, schools, workplaces, and social networks, 1970–2020

As income inequality in the United States has reached an all ‐ time high, commentators from across the political spectrum warn about the social implications of these economic changes. America, they fear, is “coming apart” as the gap between the rich and poor grows into a fault line. This paper provides a comprehensive review of empirical scholarship in sociology, education, demography, and economics in order to address the question: How have five decades of growing economic inequality shaped America's social landscape? We find that growing levels of income inequality have been accompanied by increasing socioeconomic segregation across (1) friendship networks and romantic partners, (2) residential neighborhoods, (3) K ‐ 12 and university education, and (4) workplaces and the labor market. The trends documented in this review give substance to commentators' concerns: compared to the 1970s, rich and poor Americans today are less likely to know one another and to share the same social spaces. The United States is a nation divided.


| INTRODUCTION
Since the 1970s, economic inequality in the United States has skyrocketed. While the majority of Americans have seen their wages stagnate or fall, incomes of those at the very top have grown astronomically (Atkinson et al., 2011;McCall & Percheski, 2010, p. 322;Neckerman & Torche, 2007, p. 336). In consequence, wealth has become concentrated among a small group of ultrarich Americans. Today, the top 10% takes home a third of all earnings and owns over three-quarters of all wealth (OECD, 2015, pp. 34-35). Indeed, the concentration of wealth and income in America has reached the highest level since the Great Depression (Atkinson et al., 2011;Saez & Zucman, 2016).
Commentators warn that growing wage inequality and the concentration of wealth mean that America's rich and poor are increasingly disconnected from each other. Asked about economic inequality during his presidential run, Joe Biden argued that "the gap is yawning, and it is having the effect of pulling us apart" (DePillis, 2018). Similar worries are voiced by conservatives like Charles Murray of the American Enterprise Institute. In Coming Apart: The State of White America, Murray argues that "class strain has cleaved society into two groups (…): an upper class, defined by educational attainment, and a new lower class, characterized by the lack of it" (quoted in NPR, 2012) and states that income segregation has resulted in "ZIP codes that have levels of affluence and education that are so much higher than the rest of the population that they constitute a different kind of world" (NPR, 2012). In sum, Murray (2013, p. 12) writes, "America is coming apart at the seams-not seams of race or ethnicity, but of class." Scholars have also expressed concerns that economic stratification leads the rich and poor to become segregated spatially and socially: when the gap between the rich and poor grows into a fault line, social mobility plummets, solidarity suffers, and political divisions grow deeper (Klinenberg, 2018;Lee & Bearman, 2020;Mijs, 2019;Nam, 2021;Paskov & Dewilde, 2012). As inequality and segregation become intertwined, their social impact is likely to be of much more harm to equal opportunity, democratic politics, and community life than either of the two phenomena alone. Yet, evaluating the relationship between growing income inequality and socioeconomic segregation, as theorized, is hampered by extant scholarship's focus on a single domain of life (e.g., networks or neighborhoods), which typically shows a snapshot of segregation rather than a longitudinal trend. Only by studying economic segregation in all its forms can we paint a complete picture to inform scholarly inquiry and consider appropriate policy interventions.
To document how five decades of growing economic inequality have reshaped America's social landscape, this paper offers a comprehensive empirical assessment of trends in social segregation across four realms of life: (1) friendship networks and romantic partners, (2) residential neighborhoods, (3) K-12 and university education, and (4) work and the labor market. Reviewing the long-term trends in social segregation and isolation between the rich and the poor on each of these dimensions, we ask: As socioeconomic inequalities have grown between 1970 and 2020, have rich and poor Americans become increasingly isolated?
In the following section, we build on social network analyses to document changing patterns of socioeconomic homophily and assortative mating. The studies reviewed suggest that social ties today are driven more strongly by socioeconomic status than they were in the 1970s and 1980s. Specifically in the past 30 years, people have become more likely to make friends and spend time with similarly educated others. Marriage and romantic partnership, too, is driven largely by income and education, meaning that romantic relationships are increasingly uncommon between people with different educational and income levels.
Second, we draw on literatures in sociology and social demography to summarize trends in neighborhood income segregation between 1970 and today. We find consistent evidence that segregation has grown in the past five decades. People sort into residential neighborhoods based on real estate prices, residential preferences, and racial animus, each of which can affect segregation. Much of the recent growth in economic segregation is driven by households with children, as affluent parents sort into neighborhoods with high-quality services such as good public schools.

MIJS AND ROE
Third, we explore the scholarly literature in education, sociology, and demography to describe trends in socioeconomic segregation in education. The distance between rich and poor children starts growing as early as preschool and continues through university education. We analyze how K-12 segregation among school districts, within school districts, and within schools have increased in recent decades. Next, we describe how college admissions contribute to segregated student bodies among universities and how segregation is exacerbated by selective dropout. Then, we detail the socioeconomic divide between those enrolled in the Head Start Programs versus those enrolled in unsubsidized preschools.
Finally, we draw on research in the fields of sociology and economics to discuss socioeconomic distance in the workplace. Since the 1970s, a number of forces have produced a growing polarization of jobs, solidifying the distinction between well-compensated, secure, "good jobs" and "bad jobs," defined by low-wages, nonstandard employment, and precarity. As a result, low-wage and low-educated workers increasingly do not work in the same sectors as high-wage and high-educated workers. When they do, they rarely share the same workplace.
Taken together, we find evidence in each realm of life that America's rich and poor have become more socioeconomically disconnected as income inequality has grown. The increasingly homogeneous composition of workplaces, schools, and neighborhoods limits the chances of interactions across economic fault lines. Fewer interactions result in fewer friendships and relationships, cementing the social gap as America is "coming apart." We discuss the theoretical and policy implications in our conclusion.

| NETWORKS
Networks shape a number of social outcomes, including how people find employment (Fernandez et al., 2000) and to whom they turn for advice (Small & Sukhu, 2016), financial support, and a host of other resources (Bottero, 2007, pp. 815-816;Smith et al., 2014, pp. 434, 438). In this section, we discuss whether, as income and wealth inequalities have grown, the social networks guiding interpersonal relationships have become more socioeconomically segregated, widening the distance between the rich and the poor. The social networks literature is centered on two forms of segregation: (1) homophily, or the tendency of people to establish and maintain social ties with people who are similar to themselves, and (2) assortative mating, the tendency of people to be involved in romantic relationships with others of similar social positions. By analyzing trends in homophily and assortative mating, we can draw inferences about the extent to which social segregation in the US has changed over time. For instance, if we were to see an increase in assortative mating by educational level in recent decades, we would conclude that romantic markets have become more segregated by education. As such, we draw on network analyses over time as a proxy of social segregation in key parts of people's social lives.
Status homophily is homophily centered on social demographics such as race, religion, education, and economic resources (Smith et al., 2014, p. 419) rather than, for instance, esthetic taste or political affiliation. Status homophily leads to segregation when people cluster together by social status, surround themselves with similar others, and intentionally or unintentionally keep their distance from people with different social statuses. Historically, race and religion have been the strongest sources of homophily, often stemming from prejudice and intentional exclusion (Smith et al., 2014, p. 439). However, sometimes homophily results simply from unequal social resources and opportunities for interaction in shared environments (Bottero, 2007, p. 824). For instance, on college campuses, social ties are formed between people of the same education levels by definition (Bottero, 2007, pp. 815, 818).
Similarly, in workplaces, studies show stronger social ties between employees occupying the same job level or job title (McPherson et al., 2001, p. 435). Likewise, residential economic segregation means that social ties formed in neighborhoods are often between people of similar socioeconomic status (Krivo et al., 2013). America's locally funded, district-based school system compounds this type of segregation by keeping separate students from high and low-income families (Owens, 2016). We explore segregation at work, in school, and in the neighborhood in more detail in the next three sections. The overall picture of network ties that emerges from the empirical literature is one of stability: summarizing homophily trends over the past 50 years, Marsden et al. (2020) write that, "Americans' social ties to one another underwent little overall change -remaining highly segregated along racial, socioeconomic, religious, and other axes" (Marsden et al., 2020, p. 18). Against this background, we examine the key dimensions on which assortative mating (romantic relationships between people who share the same status or background) and homophily have and have not changed.
Increasing levels of racial, ethnic, and religious diversity in the United States mean that absolute homophily has decreased (Smith et al., 2014, p. 432): As America has become more diverse, so has the typical person's social network. In line with these societal trends, Fu and Heaton (2008) find that racial and religious homogamy (marriage between people similar to one another) has steadily declined in recent decades (see ahead). However, despite an overall increase in diversity and the increased likelihood of cross-group interactions, Smith et al. (2014, p. 448) find that educational homophily in fact increased by 20 percent. In other words, while the country is becoming more diverse, social networks are becoming more divided by educational degrees. To illustrate, "the chances of a strong tie [developing] between a high school drop-out and a college graduate (i.e., an 8-year educational gap) are about as slim as a close friendship between two people with a different religion" (Smith et al., 2014, p. 448). Increasing educational homophily in modern America is driving a wedge between the educated and the uneducated, with similar implications for income and wealth, which are closely correlated to educational attainment.
Status homophily also breeds value homophily, or the tendency for people to form and maintain relationships with people with similar beliefs and values. As Lee and Bearman (2020, p. 3) find, since the 1980s, "Americans' discussion networks have become smaller, more closed, and more homophilous with respect to political beliefs." For children, the socioeconomic status of the families in which they grow up can influence their access to social capital, which in turn influences levels of trust, civic engagement, religious involvement, and informal socializing (Wright, 2015, p. 642). Looking at trends in survey data from 1976 to 2009, parental education levels are strongly associated with participation in activities such as community service and church-going (Wright, 2015, p. 647). For example, while community participation has increased at all levels, it is most pronounced among children from the top third of educational achievement (Wright, 2015, p. 647).
Assortative mating -be it through marriage or other types of romantic relationships -provides another lens through which social networks scholars examine segregation. As Schwartz (2013, p. 452) puts it, "boundaries between social groups are maintained through assortative mating and weakened through intermarriage. Thus, the degree to which populations intermarry tells us about openness of social boundaries." Historically, homogamy has been defined most by religion and race. Over time, however, as parents and Church figures lost influence and online dating took off, romantic relationships have become determined by individual characteristics like education and income (Schwartz, 2013, p. 454). As such, "marrying down" to someone with a lower education level or income has become increasingly uncommon, undesirable, and perceived as "risky," seeing as an equal or higher spousal education level would boost household income and financial security (Schwartz, 2010(Schwartz, , p. 1527. Educational homogamy has become more pronounced as women started to join the workforce in large numbers since the 1970s. The male breadwinner model has lost ground, and women are increasingly expected to contribute to household income and "pull their own weight" (Mare, 1991, p. 17;Schwartz, 2010Schwartz, , p. 1527. Status-driven partner selection is a major part of why homogamy has increased in recent decades. Kopf (2020) draws on US census data to show that homogamy is especially strong at the top of society: Whereas only 0.4% of married couples in 1960 both made the top 20% of their age group's income, in 2018, that number had increased to 7.4%. If couples married without considering each other's income, the number would be half that. Looking at assortative mating from an educational standpoint, Eika et al. (2019) find that homogamy among lower-educated Americans is most pronounced and has increased gradually since the 1960s. Whereas, in the early sixties, Americans without a high school degree were 60% more likely to marry a person in the same educational group, in 1980 they were 160% more likely, and by 2013, people without a high school degree were 620% more likely to marry a person without a high school degree than someone with a degree (Eika et al., 2019, p. 2799).

MIJS AND ROE
One mechanism through which homogamy can come about is through "winnowing," which refers to increasing selectivity in partner choice as couples move from casual dating to more serious romantic relationships, including marriage. Drawing on retrospective data on couple formation, Blackwell and Lichter (2004, p. 725) find pronounced levels of educational homogamy: Americans without a high school degree are 50 times as likely to marry another person without a high school degree than they are to "marry up," and people with a professional degree or higher are 16 times more likely to marry a similarly educated person than to "marry down." However, they find only modest evidence of winnowing: compared to homogamy, people are a little more likely to cohabitate in mixededucation couples, but they are just as unlikely to date across educational lines as they are to marry. Mare (2016) attributes the steady growth in educational assortative mating to two factors. First, rising average age at marriage means that couples today are better able to assess their partners' educational achievements compared to younger couples whose ultimate educational level has not yet been established (Mare, 2016, p. 134).
Second, increasing economic returns to education have more closely linked educational levels, economic security, and life chances.
A countervailing trend stems from the advent of online dating, which paints a very different picture of assortative mating. Today, over a fifth of new US romantic couples and a majority of same-sex couples met each other online (Rosenfeld & Thomas, 2012). Online dating has become an increasingly common way for couples to meet, especially for those seeking partners in "thin markets" such as gays and lesbians, as well as middle-aged heterosexuals (Rosenfeld & Thomas, 2012). Because online platforms typically filter potential "matches" based only on age and geographic location (i.e., not by socioeconomic status or education), dating app and website users are exposed to more diverse groups of potential partners than they would typically meet offline (Thomas, 2020; for a transatlantic comparison, see Potarca, 2020).
As a consequence, studies suggest, the growing prevalence of online dating may reduce assortative mating.
Drawing on data collected in 2009 and 2017, Potarca (2017) finds that romantic partners who met online are indeed more likely to be interracial, interreligious, and "inter-educational" couples than those who met offline. At the same time, some online dating platforms have normalized partner selection based on racial and ethnic preferences by allowing users to filter out particular racial or ethnic groups. This has led to racial disparities in partner selection and barriers to finding a "match" for Asian men and black women specifically, as described in a new book by Curington et al. (2021) and as acknowledged by Christian Rudder (2014), cofounder of the popular dating platform OkCupid. Evidence from Europe suggests that educational homophily may be as prevalent on platforms that allow users to include it in their filters of romantic matches (Skopek et al., 2011). In fact, US platforms like The League are designed specifically to help people with elite credentials find matches with those similarly credentialed.
Thus, while trends in socioeconomic assortative mating and homophily have increased in past decades, there are some indications -and counterindications -of these trends to be offset by online dating. Future research will tell what role online platforms will play.

| NEIGHBORHOODS
Economic segregation is the "geographic manifestation of income inequality" (Jargowsky & Wheeler, 2017, p. 2), the sorting of households into neighborhoods by social class or income. By reviewing research on residential income segregation, we document how the rich and poor are physically disconnected from each other (Krivo et al., 2013).
We dedicate the first part of this section to discussing the quantitative trends and debates regarding how much neighborhood segregation has changed since the 1970s. Next, we discuss the causes, consequences, and intergenerational persistence of neighborhood segregation.
Since 1970, income inequality among neighborhoods has increased more rapidly than income inequality among households (Jargowsky & Wheeler, 2017 like New York and Philadelphia have seen greater increases in neighborhood segregation than others (Jargowsky, 2018, p. 223). As income inequality in the United States increased by 15% over the 1970-2010 period, inequalities among neighborhoods in these cities grew by about 40% (Bischoff & Reardon, 2014, pp. 222-224).
During this period, the 1980s experienced a particularly sharp growth in economic segregation, which slowed down in the 1990s, likely due to the increasing number of mixed-income housing developments in urban areas and the demolition of large, high density, low-income housing projects (Reardon & Bischoff, 2011, p. 1139. In the 2000s, levels of segregation increased again as income inequality grew, except for a brief fall following the Great Recession (Bischoff & Reardon, 2013, p. 5;Jargowsky & Wheeler, 2017, p. 9).
While the rise of residential segregation is virtually undisputed, there is some debate over the precise estimate of neighborhood segregation, especially in the period after 2000. One source of contention stems from the fact that many studies measure economic segregation based on income data reported in the US decennial long-form census While Reardon and Bischoff (2016) found an 8% increase in rank-order income segregation between 2000 and 2012, Reardon et al. (2018) found only half that increase after correcting for bias due to the change to ACS data (p. 2153). Notwithstanding this period-specific correction, looking at the long trend from 1970 to 2012, the authors' bias-corrected estimates show a 25% increase in income segregation in the United States (Reardon et al., 2018(Reardon et al., , p. 2153), a figure close to the uncorrected estimate of 27% reported in Bischoff and Reardon (2013) and Reardon and Bischoff (2016).
Traditionally, research on segregation has focused on the extent to which poverty and affluence are concentrated spatially (Quillian, 2012, p. 355;Reardon & Bischoff, 2011, p. 1097. Such is the case when wealthy families are surrounded by other wealthy households, while poor families are isolated from middle-and high-income households (Krivo et al., 2013;Wang et al., 2018). Scholarship shows how residents of poor neighborhoods are also more likely, in their daily routines for work, and as part of their social life, to frequent other poor neighborhoods, compounding their socio-economic isolation (Levy et al., 2020;Wang et al., 2018). Whereas concentrated poverty was the main driver of segregation in the 1970s and 1980s, more recent research finds that concentrated affluence may be a greater source of the growing levels of income segregation that accompany the rise of top incomes (Reardon & Bischoff, 2011, p. 1138. A combination of personal preferences and economic factors sort people into the neighborhoods in which they live. High-rent neighborhoods are out of reach for the less affluent because of market prices and the unavailability of mortgage loans. The market itself perpetuates income segregation because housing prices are influenced by the cost of nearby housing (Reardon & Bischoff, 2011, p. 1097.
Therefore, an expensive house is likely to be situated nearby equally expensive houses, spurring further segregation.
Segregation is driven especially by the growing spatial separation of rich and poor families with children, as parents with the required economic resources move to areas with good public schools, safe neighborhoods, and access to high-quality services like libraries, parks, and childcare providers (Owens, 2016, p. 565;Sharkey, 2008, p. 936). In a study of America's 100 largest metropolitan areas, Owens (2016, p. 565) finds that residential income segregation was fueled almost entirely by families with children, for whom residential income segregation grew by about 20% between 1990 and 2010. Over this time period, segregation of childless households, which account for two-thirds of the population, has remained more or less stable at half the rate of households with children (Owens et al., 2016, p. 565).
Residential segregation is also driven by racial animus. As a consequence of economic inequalities among racial groups and racialized lending and real-estate practices, black low-income families more frequently live in highpoverty areas than do white families with similar levels of income (Owens, 2018, p. 2). Much of racially patterned neighborhood sorting can be attributed to white flight and increasing suburbanization in past decades as white families have moved to predominantly white districts to avoid having minority or low-income neighbors 6 of 16 -MIJS AND ROE (Jargowsky, 2018, p. 225). Social policies in past decades like zoning, school assignment policies, and the construction and distribution of different types of housing have contributed to suburban sprawl and racial segregation (Jargowsky, 2018, p. 224;Rothwell & Massey, 2010, p. 1123. Expansion of highways and transportation options similarly allows wealthy families to live in suburbs while still being able to commute to jobs in cities (Reardon & Bischoff, 2011, p. 1140. Whatever its causes, neighborhood segregation tends to persist across generations. Sharkey (2008) describes how children are likely to grow up and live in neighborhoods very similar to the ones in which they were raised. Indeed, destination neighborhoods are best predicted by origin neighborhoods, beyond any other family background factor or a person's educational attainment (Sharkey, 2008, p. 962, 953). In his book Great American City, Sampson (2012) similarly describes the inertia and durability of economic segregation and concentration of poverty. He notes that most poor neighborhoods in Chicago in 1970 have remained poor some 30 years later, even though the metropolitan area on the whole had become more diverse (Sampson, 2012, p. 344). These persisting boundaries among neighborhoods produce social exclusion by separating racial groups and social classes both physically and socially, thereby limiting interactions across fault lines (Levy et al., 2020). Consequently, it is unsurprising that many people lack neighborhood ties to people from different socioeconomic groups throughout their lifetimes. This holds truer today than at any point in the past half-century.

| SCHOOLS
Despite the 1954 ruling in Brown v. Board of Education of Topeka, American schools remain both separate and unequal, albeit in different and subtler ways. While legal mandates mean that racial separation in schools can no longer be absolute, many schools and school districts continue to be segregated, both racially and socioeconomically (Fiel & Zhang, 2019;Orfield et al., 2019;Reardon & Owens, 2014). In this section, we discuss trends in segregation among and within schools at the preschool, secondary (K-12), and tertiary level. We consider segregation among districts and among schools, tracking of students within schools, and reasons why colleges remain socioeconomically homogeneous places.
The US public K-12 school system is funded by local property taxes, and students are assigned to public schools based on geographically zoned school districts (Duncan & Murnane, 2011;Lareau & Goyette, 2014). School segregation can manifest itself both among districts and among schools within a given district. Because school districts are segregated, so are schools. As we have seen, residential segregation has increased in recent decades, which raises the question as to whether school segregation has increased at a similar rate. In this paragraph, we discuss school segregation within districts. Trends in within-district segregation are generally based on school-level data on students' eligibility for the National School Lunch Program (family income within 130% of the poverty line), as a rough indication of socioeconomic background (Reardon & Owens, 2014, p. 7). From what limited data are available, Altonji and Mansfield (2011) conclude that school segregation has indeed followed the trend in residential segregation, growing at an especially fast rate in the 1970s and 1980s and declining again in the 1990s. This conclusion is corroborated by Reardon and Owens (2014, p. 7), who find that, since 1990, socioeconomic segregation has increased among districts, but levels of segregation among schools within a given district have changed only marginally. Owens et al. (2016) argue that economic segregation in schools did continue to increase in the 1990s, especially in elementary grades and in large school districts. According to these authors, school segregation stalled only after 2000 and did not change between that time and 2012.
In contrast to segregation within school districts, socioeconomic segregation among school districts can be more readily assessed. Scholars typically draw on census data on family income for school-age students in each US school district (Bischoff & Owens, 2019, p. 1642Reardon & Owens, 2014, p. 7). Between-district school segregation among public school students increased during the 1990s and 2000s in 75 of the 100 largest metropolitan areas, a trend most pronounced by the growing isolation of poor children from children in middle and high-income MIJS AND ROE -7 of 16 families (Owens, 2018;Reardon & Owens, 2014, p. 205). Strikingly, the most educated states are often also the most segregated. For instance, Massachusetts (a state with a high level of educational attainment) has one of the highest levels of income segregation among school districts, whereas Louisiana, where levels of educational attainment are considerably lower, has a much lower level of income segregation (Bischoff & Owens, 2019, p. 1648. School segregation separates students both from other students and from adults of different socioeconomic groups. In a longitudinal study, Bischoff and Owens (2019) measured how students from different socioeconomic backgrounds had different levels of exposure to adults with at least bachelor's degrees and to adults experiencing unemployment. They find a large gap between poor and affluent children (tenth and first decile of the family income distribution, respectively) in exposure to highly educated adults, increasing from 7.3 in 1990 to 11.3 percentage points in 2014 (Bischoff & Owens, 2019, p. 1648. This exposure gap adds to existing disparities among school districts. Scholars estimate that compensating for social advantages in high-income districts would require states to increase funding to low-income districts by anywhere between 5% and 160% (Duncombe et al., 2015).
Another mechanism through which students are segregated is educational tracking, which is the practice of sorting students into different instructional groups within their schools based on assessments of their academic ability (Domina et al., 2017). Historically, secondary school students were assigned to academic, general, or vocational tracks (Hallinan, 1994, p. 79). Today, schools more commonly separate students by course levels, such as advanced, honors, regular, or basic courses in English, math, and sometimes in social studies, science, languages, and other courses (Domina et al., 2019). While proponents of tracking argue that it allows teachers to tailor instruction and pace to students' abilities, minority and low-income students are assigned to lower tracks at much higher rates than their peers, even after taking into account their ability (Van de Werfhorst & Mijs, 2010). Therefore, tracking works to segregate students into separate groups and classrooms within the same schools. Vocational track students frequently receive lower quality teaching that hinders their academic achievement. Another important consequence of tracking is its effect on students' social networks. Kubitschek and Hallinan (1998, p. 3) showed that tracking significantly affects students' friendship choices due to propinquity, similarity, and status. Therefore, if tracking is closely linked to socioeconomic status, then friendships, too, will develop along socioeconomic lines.
These socioeconomic disparities often go together with racial segregation. As of 2005, 88% of high minority K-12 public schools (>90% minority students) were also high poverty schools, with more than half of students on free and reduced lunch programs (Frankenberg et al., 2019, p. 23;Orfield & Lee, 2005, p. 16). While court-ordered desegregation in the 1960s and 1970s has weakened the link between race and class (Reardon & Owens, 2014, p. 7), progress toward integration has been undermined by "white flight" to majority-white school districts and to private schools (Clotfelter, 2004;Fiel & Zhang, 2019). Reber (2005, p. 571) estimates that racial integration in schools would have been a third higher during the 1960s and 1970s, were it not for decreasing white enrollment in school districts with high numbers of black students. "Affluent flight" describes an analogous process whereby parents who can afford it enroll their children in private schools to escape public schools in high-poverty areas (Saporito, 2003;Saporito & Sohoni, 2007). To illustrate the trend in racial segregation, the proportion of schools that are intensely racially segregated (>90% non-white students) has more than tripled, from less than 6% in 1988 to over 18% in 2016 (Frankenberg et al., 2019, p. 21).
While not too much is known about socioeconomic segregation in preschool, we can use official data to describe how preschool enrollment reflects the demography of the US population. The most recent National Center for Education Statistics (National Center for Education Statistics, 2017) show that among parents with less than a high school degree, a quarter of children are enrolled in preschool. Of college-educated parents, almost half of the children go to preschool. Absent more detailed information, we conclude that preschools are composed predominantly by children of higher socioeconomic backgrounds. Low-income children, meanwhile, are drawn to Head Start Programs, which are socioeconomically segregated by design, purposely targeting low-income families (Cascio & Schanzenbach, 2013). In other words, socioeconomic segregation starts as early as preschool.

MIJS AND ROE
Turning now to the tail end of the educational experience, over the past 40 years, the correlation between family income and college attainment has grown stronger in spite of college initiatives to increase diversity and make available financial aid and fellowships (Alon, 2009;Bastedo & Jaquette, 2017;Ellwood & Kane, 2000;Goldrick-Rab et al., 2016, p. 1764Haveman & Smeeding, 2006). Although low-income students have made substantial academic gains since the 1970s, higher income students have made even stronger gains. Consequently, it has become more difficult for lower income students to compete in the college admission process (Bastedo & Jaquette, 2017). While 30% of children from families in the bottom income quartile enroll in college, among families in the top quartile, that number is 80% (Goldrick-Rab et al., 2016, p. 1764. Across colleges, about a fifth of students come from families with annual incomes below $25,000 (in 2001 dollars), but only 6% of students in the 100 most selective colleges do (Reardon et al., 2012, p. 6). In fact, Chetty et al. (2017) calculate that students from the richest 1% are 77 times more likely to attend an Ivy League institution than students from the poorest fifth of the population. Indeed, since 2000, there has been almost no growth in the student population from the bottom 20% of the income distribution at Ivy League schools and other elite colleges (Thompson, 2017).
These disparities in higher education are exacerbated by the fact that a high number of low-income students who do enroll in college do not reach graduation (for a review, see Jeffrey, 2020). Nationally, 84% of Pell Grant recipients drop out before graduation (Goldrick-Rab et al., 2016, p. 1764. Furthermore, there is a pattern of "undermatching" of low-income students, meaning that low-income students with identical academic achievement to high-income students matriculate to less selective colleges (Chetty et al., 2020, p. 2): High-income students are 34% more likely to attend selective colleges than low-income students with identical test scores. Similarly, students from families in the top income quartile enroll in highly selective colleges at seven to eight times the rate of students from families in the bottom income quartile (Reardon et al., 2012, p. 7). As powerfully documented by Armstrong and Hamilton (2013), what little economic diversity exists in these colleges is further limited by a lack of cross-class friendships and class barriers to participation in sororities and fraternities.

| WORKPLACES
The realm of work is marked by two types of segregation, both of which occur along socioeconomic lines. The first concerns the division between highly educated and low-educated workers in the workplace (Barth et al., 2016).
Based on population data covering all US workers from 1978 to 2019, Song et al. (2019) describe how growing income inequality is reflected by a widening gap among firms in the kinds of workers they employ: Over the last 40 years, employee sorting and segregation has meant that (1) high-paid workers now increasingly work for highpaying firms, and (2) high-wage workers are increasingly likely to work with each other, while low-wage workers are clustered in different firms and workplaces altogether (Song et al., 2019, p. 46; see also Tomaskovic-Devey et al., 2020).
As Weil eloquently puts it, "like a rock with a fracture that deepens and spreads with time, the workplace over the past three decades has fissured" (Weil, 2014, p. 7). While Weil's focus is on fissures in the workplace resulting from outsourcing labor previously done within firms, Song et al. (2019) describe how the segregation of low-wage and high-wage workers also results from the rise and fall of different companies and industries (Barth et al., 2016;Handwerker, 2015). As Kremer and Maskin (1996) observe, "[O]ver time, it has become less common for high-and low-skill workers to work in the same firm. Economic activity has shifted from firms such as General Motors, which use both high-and low-skill workers, to firms such as Microsoft and McDonald's, whose workforces are much more homogeneous" (Kremer & Maskin, 1996, p. 1).
A second line running through the American labor market is that between, as Kalleberg (2011) puts it, "good jobs" and "bad jobs." Since the 1970s, international competition, government deregulation, weakening labor unions, and the rise of the service sector have conspired to produce a growing polarization of wages and job quality (Autor & Dorn, 2013;Kalleberg, 2011), further exacerbated by the Great Recession in the late 2000s (Rothstein, 2017). On one side of the divide, we find a declining number of jobs with high compensation, generous benefits, relative autonomy, and security, which require exceedingly high levels of education and elite credentials (Atkinson et al., 2011;Wilmers & Aeppli, 2021). On the other, there is a growing supply of precarious employment marked by low wages, little to no benefits, a lack of control and security, and temporary contracts (Crowley et al., 2010;Kalleberg et al., 2000;Lyness et al., 2012). Low-wage workers experience far more work hour volatility from week to week and month to month than do their high-income counterparts (Henly & Lambert, 2014;LaBriola & Schneider, 2020). Such precarity and volatility are documented by Halpin's (2015) case study of a high-end food- Increasing distance between the two sides of the labor market and low levels of mobility in-between mean a growing gap in circumstance as well as contact: low-paid and low-educated workers find employment in different job sectors (Kalleberg et al., 2000), at different kinds of firms (Holzer, 1999) and through different means (Purser, 2019;Sugie, 2018) than their highly educated and better-compensated counterparts (Binder et al., 2016;Rivera, 2015). Inequalities are increasingly driven by where you work, and where you work has increasingly come to determine with whom you work.

| CONCLUSION
This paper describes levels and trends of socioeconomic segregation between the 1970s and today against the background of growing economic inequalities. Reviewing research in sociology, education, demography, and economics covering five decades of scholarship, we find different levels but remarkably similar trends in segregation across four distinct domains of social life. Segregation along the lines of education, income, and social class has grown in recent decades, as expressed in the friends we have and make, the romantic partners we choose, the neighborhoods in which we live and where our children grow up, the schools we and they attend, and the workplaces in which we come to spend much of our days.  Figure 1 gives a visual summary of key trends across these domains based on available data from 1970 to 2010.
As the income gap, indexed by the Gini coefficient of household income inequality, grew by 14%, levels of socioeconomic segregation increased at least as much (Jargowsky & Wheeler, 2017): rates of network homophily and homogamy increased by about 18% (Schwartz & Mare, 2005;Smith et al., 2014), and income segregation among neighborhoods grew by more than a third (Jargowsky & Wheeler, 2017). Rivaling the growing share of income held by the top 1% (Piketty et al., 2018), between-firm wage segregation increased by more than half (Song et al., 2019), and between-district socioeconomic segregation among families with children grew by almost 70% (Owens, 2016).
The documented trends give substance to concerns about America's "coming apart." As the joint growth of income inequality and segregation turns material divisions into social divisions, rich and poor Americans are increasingly unlikely to know one another or share the same spaces. When individuals across the income divide become entrenched in their own ways of life, among their own kinds of people, we are likely to see solidarity suffer (Paskov & Dewilde, 2012), trust fall (Barone & Mocetti, 2016), and politics polarize (Lee & Bearman, 2020). These findings speak directly to the theorized relationship between economic inequality and segregation which, when intertwined, consolidates the advantages of the rich, compounds the disadvantages confronting the poor, and erodes opportunities for social mobility (Corak, 2004(Corak, , 2013Nam, 2021).
Ironically, when the rich and the poor lead disconnected lives, neither can see their unequal society for what it really is (Edmiston, 2018;Minkoff & Lyons, 2017). The segregated nature of inequality may be the key to understanding why Americans systematically underestimate the extent of inequality in their society and overstate its meritocratic nature (Alesina et al., 2018;Mijs, 2018;Norton & Ariely, 2011). The political consequence, as Mijs (2019, p.25) has argued, is that democratic publics "may find themselves stuck in a feedback loop where more inequality paradoxically leads them to experience less of it-and care less about it." In other words, the close link between inequality and segregation may help explain the muted political response to America's growing income and wealth gap (see also Kelly & Enns, 2010).
It follows that addressing growing inequality politically is unlikely to succeed without reckoning with the economic divisions running through American society. Creating awareness of inequality and generating public support for addressing it starts with socioeconomically integrating neighborhoods, schools, and workplaces and (re) establishing public places for cross-class interactions-what Klinenberg (2018) calls Palaces for the People: childcare centers and churches, parks and public libraries are crucial parts of the social infrastructure where people of all backgrounds can meet, casually interact, forge bonds, and find support (Small, 2009(Small, , 2017. Key to that challenge are the formative institutions where young people begin to learn about their society. In the absence of exposure to economic diversity, young people will grow up with a naïve understanding of American meritocracy in a country that is increasingly divided along socioeconomic lines.