We tested the hypothesis that instrumental learning is impaired in children with attention deficit/hyperactivity disorder (ADHD) and tested whether this deficiency can be ameliorated by the use of three different doses of methylphenidate (MPH): a low, a medium, and a high dose. Fifty children (23 with ADHD, 27 typically developing) performed an instrumental learning task in which they had to map four stimuli to two responses using feedback that differed in information value and that was coupled to monetary gain (€0.2). Feedback was either contingent, thus fully informative on performance, or probabilistic, and informative in only 88 % of the trials. Dependent variables were response accuracy and latency. Contrary to predictions, children with ADHD and typically developing controls did not differ in their ability to acquire the stimulus–response mappings, in either condition. This indicates that with a simple instrumental learning task, children with ADHD are able to learn from rewarded feedback, as controls do, suggesting that children with ADHD are capable of learning both at home and in class when the environment is adequate. Possibly, learning problems are more evident in children with comorbid ODD, as exploratory analyses indicated that accuracy scores were significantly reduced when children with ADHD exhibited high levels of parent-rated ODD symptoms. Medication analysis showed that children with ADHD completed the task more accurately and faster when taking MPH compared to placebo, particularly when the dose was high.
