OBJECTIVE To examine the specificity of methylphenidate effects on the processes that support the ability to rapidly and accurately coordinate the performance of multiple tasks in children with attention-deficit hyperactivity disorder (ADHD). METHODS Twenty children with ADHD performed the task-switching paradigm while on and off medication. The paradigm involves switching between two different tasks, discriminating the value of a number presented on a computer screen and deciding how many numbers were present on the screen. The children also performed single-task control conditions. RESULTS Analyses of variance indicated the medication selectively enhanced the children's ability to rapidly and accurately switch between tasks and to focus attention on the currently relevant response set. CONCLUSIONS This study helps to elucidate the nature of methylphenidate effects on the cognitive processes which support the ability to coordinate the performance of multiple tasks. Medication appears to selectively enhance inhibitory processes which support task-switching.