This paper examines the effects of the Fast Track preventive intervention on youths' functioning in three domains: disruptive behavior problems, involvement with deviant peers, and social skills during the middle school years. Eight hundred ninety-one children had been randomly assigned by sets of schools within four sites to intervention (n = 445) or to control (n = 446) conditions. In contrast to prior findings of the effectiveness of the Fast Track intervention during the elementary school years, the current findings indicate that Fast Track had little overall impact on children's functioning in these domains during this age period. There were positive intervention effects on only 2 of 17 outcomes examined. Although the intervention had positive impact on children's hyperactive and self-reported delinquent behaviors in seventh grade, there were no intervention effects on other externalizing behavior problems or on social skills, and there was a negative intervention effect on children's involvement with deviant peers during this age period. (Contains 3 tables and 2 figures.)