Disruptive kindergarten boys from inner-city low socioeconomic neighborhood schools were randomly allocated to a preventive intervention and control condition. The 2-year prevention program included a home-based parent training component and a school-based social skills training component. Participants were followed up to mid-adolescence. Results indicated that a significantly greater percentage of treated boys remained in an age-appropriate regular classroom up to the end of elementary school and that the treated boys reported significantly less delinquent behaviors at yearly assessments from 10 to 15 years old, compared with controls. The preventive intervention appeared to have a significant long-term impact on the social development of the disruptive kindergarten boys. Earlier and more intensive intervention may be necessary for some cases, whereas for all disruptive boys, booster sessions between 12 and 15 years of age are recommended.