This study aims at investigating the direct effects of methylphenidate on school performance of primary school children. Although behavioral effects of this frequently prescribed drug are thoroughly studied (and confirmed), the effects of methylphenidate on school performance are less clear. Recent overviews indicate that effects are mainly quantitative and subject-specific. To gain more insight in this issue, the current double blind placebo controlled crossover study investigates not only the effects of methylphenidate on school performance but also it's effect on related variables such as short term memory, motivation and behavior. 60 children with ADHD are included and tested twice (with medication and with placebo) at their primary school.