This study evaluated the separate and combined effects of behavior modification and 2 doses of methylphenidate (MPH; 0.3 and 0.6 mg/kg) compared with baseline (no behavior modification and a placebo) on the classroom behavior and academic performance of 31 ADHD (attention deficit-hyperactivity disorder) boys attending a summer treatment program. Results revealed significant effects of both interventions, with the mean effect size of medication being more than twice as great as that of behavior modification. Relatively small incremental value was gained by the higher dose of medication or the addition of behavior modification, compared with the effects of the low dose of MPH. In contrast, the addition of either dose of MPH resulted in improvement beyond the effects of behavior modification alone. These group effects reflected those obtained in analyses of individual differences. Furthermore, comparisons of individual responsiveness showed that boys who responded to one treatment also responded to the other.