 Participants attend a summer treatment program each Monday-Friday for 9 weeks. They participate in group recreational and classroom activities, with 12 children and 5 staff per group. Three behavioral conditions no behavioral modification, low-intensity behavioral modification, and high-intensity behavioral modification are delivered in random order, with each condition lasting 3 weeks. Along with the behavioral treatment conditions, children receive 1 of 4 medication doses placebo, 0.15 mgkg methylphenidate, 0.3 mgkg methylphenidate, or 0.6 mgkg methylphenidate in random order, with each dose varied daily and repeated 3 or 4 times within each behavioral treatment condition. 