Although attention deficit hyperactivity disorder (ADHD) is among the most heritable psychiatric childhood disorders, social and gene-environment interactions seemingly play an important role in the etiology of ADHD. Consistent with this, this study finds that School-Wide Positive Behavioral Interventions and Supports (SWPBIS) reduced the likelihood of pharmacotherapeutic treatment for ADHD at age 14-16 by 12%, using population-wide Norwegian register data and a difference-in-difference design (N = 698,364, birth cohorts 1990-2002, 48.7% girls, 5.7% immigrant background). At-risk students in schools with high fidelity of implementation are driving these intervention effects. Overall, the findings indicate that children with a genetic disposition for ADHD are more likely to avoid medical treatment in an organized and predictable school setting with a focus on positive reinforcement.