Objective: Accumulating evidence highlights the importance of using psychosocial approaches to intervention for children with attention-deficit/hyperactivity disorder (ADHD) that target the family and school, as well as the intersection of family and school. This study evaluated the effectiveness of a family-school intervention, Family-School Success (FSS), designed to improve the family and educational functioning of students in Grades 2-6 who meet criteria for ADHD combined and inattentive types. Key components of FSS were conjoint behavioral consultation, daily report cards, and behavioral homework interventions. Method: FSS was provided over 12 weekly sessions, which included 6 group sessions, 4 individualized family sessions, and 2 school-based consultations. Participating families were given the choice of placing their children on medication; 43% of children were on medication at the time of random assignment. Children (n = 199) were randomly assigned to FSS or a comparison group controlling for non-specific treatment effects (Coping With ADHD Through Relationships and Education [CARE]). Outcomes were assessed at post-intervention and 3-month follow-up. The analyses controlled for child medication status. Results: FSS had a significant effect on the quality of the family-school relationship, homework performance, and parenting behavior. Conclusions: The superiority of FSS was demonstrated even though about 40% of the participants in FSS and CARE were on an optimal dose of medication and there were significant time effects on each measure. This relatively brief intervention produced effect sizes comparable to those of the more intensive Multimodal Treatment Study of Children With ADHD (MTA) behavioral intervention. (Contains 2 figures and 4 tables.)