The main trial or Phase II, beginning in 1991 and ending in 1994, included two study groups, an Intervention Group and a Control Group, with a total of approximately 8,000 students. The measurement cohort included 5,107 students. The Intervention Group received a school-based program consisting of the CATCH curriculum, the physical education program, the school food service program, and programs to establish smoke-free schools. One-half of the Intervention Group received the same school-based program plus a family-based program. The Control Group received the usual health curriculum of the control schools but none of the CATCH interventions. The primary endpoints at the school level were reduction in fat and saturated fat in school lunches and increased moderate to vigorous activity in PE classes. The primary endpoint at the student level was serum cholesterol change between the third and fifth grades. Secondary endpoints included health knowledge, self-efficacy and behavioral skills that related to the adoption and maintenance of cardiovascular health behaviors; dietary fat intake; dietary sodium intake; physical activity; and systolic blood pressure. The unit of randomization was the elementary school. Schools were recruited for participation and then randomly assigned to the study groups. Twenty-four schools were recruited from each of the four participating field centers for a total of 96 schools. In each center, ten of 24 schools were assigned to the Control Group and 14 to the Intervention Group. Among the 14 intervention schools, seven were randomly assigned to the school-based intervention alone and seven to the school-based and family component. Measures of behavioral outcome and process variables were made during each grade from three through five. Physiological measurements were made at baseline in grade three and at the end of grade five. Final measurements were completed in May 1994. Close-out and final data analysis were conducted in the latter part of 1995 and in 1996. The major results paper was published in JAMA in March 1996. Ten major mainstream papers were published in Preventive Medicine in 1996.