The second phase examines the immediate and longer term effects of prevention intervention to improve children's social behavior and communication skills. Three-year-old children (n=180) that are attending community daycares or therapeutic nurseries serving low-income families, and that have mild to moderate language delays and patterns of parent-child interaction associated with poor behavioral outcomes will be recruited. One hundred and eighty children at high risk for development of conduct disorders and related behavioral problems will be randomized to either an intervention group (n=90) or an untreated control group (n=90). Three successive cohorts of children and families will be randomly assigned to treatment or control groups; each cohort will be followed three years until the child enters kindergarten. The primary intervention will include parent training in communicative interactions and behavior management and direct intervention with the child to teach social communication skills in peer interactions. Secondary intervention will include classroom consultation, maintenance of parent training and child intervention as needed, family support and liaison services, and assistance during child transition into kindergarten. Local Head Start collaborators are included in all phases of the trial. The outcomes of the trial will be examined at four points - immediately after the study period is completed, 6 months later, 1 year later, and 2 years later. The last assessment will focus on academic, social, and mental health outcomes at the end of the children's kindergarten year. Positive effects on children's problem behaviors, social skills, and overall development and positive effects on parent-child interaction are expected to be associated with participation in the treatment condition.