Rationale: ADHD (attention deficit hyperactivity disorder) is a common childhood developmental disorder. Besides the behavioural symptoms of ADHD, many children with ADHD experience problems with academic activities. More specifically, these children show problems with math, spelling and reading. The most common treatment for ADHD is medical treatment with methylphenidate (MPH). This treatment is effective in the reduction of ADHD symptoms. However, it is unclear whether treatment with MPH can also improve academic activity. If MPH improves academic activity, it is of great interest to understand which variables influence or mediate this effect. The results from this study can give more insight in the working mechanisms and effectiveness of MPH in reducing the academic problems commonly observed in children with ADHD.