Various patterns of antisocial behavior were identified over three data-collection waves. Three groups were identified according to their level of antisocial behavior: "low/non-antisocials" (n=844); "experimental" (n=88); and "persistent" (n=131). No distinctive groups based on antisocial behavior emerged until the beginning of primary school (5-6 years old). Significant and consistent differences existed between the "persistent" and "low/non-antisocial" group from this time-point. The "experimental" and "low/non-antisocial" groups did not differ significantly until early adolescence. Differences in group members were related primarily to temperamental characteristics and behavioral problems. Group differences were evident in the areas of social competence, association with deviant peers, school adjustment, maladaptive coping styles, and involvement in risk-taking activities. The findings suggest that parents, teachers, clinicians, and policymakers should focus on the early primary school years as a critical time for intervention in attempting to prevent the development of persistent antisocial behavior. The early intervention programs that have been most effective have been multifaceted, involving teacher and parent training in behavior-management skills, such as monitoring a child's behavior, using effective discipline, and promoting prosocial behaviors. Teaching children social, cognitive, and problem-solving skills has also been important. 7 tables and 17 references