The data reported here are part of a 3-year planning study in preparation for a longitudinal study of the development of antisocial behavior. The 210 families involved in this study included 74 boys ages 9-10, 78 boys ages 12-13, and 58 boys aged 15-16 and their parents. All but one of the boys were white. Phase 1 of the study involved the collection of teacher ratings and peer nominations. Phase 2 consisted of a 3-hour structured interview with parents and children separately. They also completed questionnaires and participated in a 30-minute structured videotaped family problem-solving task. During phase 3 of the data collection, telephone interviews and home observations were conducted. The study found that both family and peers contributed to the child's performance of antisocial, delinquent behavior. The nature and relative weight of their influence shifted as the child moved from preadolescence to late adolescence. Initially, the family's failure to teach a young child social skills and to discipline antisocial behavior was central. This fostered the child's association with deviant peers who provided further training in antisocial behavior. The findings suggest that if parents fail to monitor their child's peer choices, his behavior, and the amount of time he is unsupervised, his drift into deviancy will probably continue and perhaps exacerbate his risk for maladjustment and an antisocial lifestyle in adulthood. 4 tables, 1 figure, and 38 references