The effects of participation following a 3-year preventive intervention trial targeting elementary school children with early-onset aggressive behavior were evaluated. Intent-to-treat analyses revealed that program participants, compared with controls, showed greater gains in social skills, academic achievement, and parent discipline, with mean scores in the normative range on the latter two constructs. As-intended participation in the Family Program, which included separate parent and child education and skills-training groups, was associated with improved parent discipline practices and gains in children's social skills, with level of child aggression moderating gains in academic achievement. Recommended level of FLEX family support contact time was associated with gains in academic achievement, concentration problems, and social skills, with parents of severely aggressive children showing greater reductions in parent distress.