The aim of the MiA-Study is to address the current lack of effective treatment options to reduce cognitive and physical long-term problems in children and adolescents with Attention Deficit Hyperactivity Disorder (ADHD). Through the use of the Mio-Training, cognitive development will be strengthened and metacognitive thinking and awareness will increase. The MiA-Study is conducted additionally to the Mio-study to evaluate the effectiveness of the Mio-Training specifically within the ADHD population. The Mio-Training for children and adolescence with ADHD includes a combination of cognitive and coordinative training tasks and prospective as well as retrospective metacognitive questions. In a randomized controlled trial, the Mio-Training will be analysed for its efficacy on metacognitive thinking and executive functions. In particular, the investigators are interested in factors that affect the efficacy of the training program such as compliance, age, sex or the severity of the ADHD. This study will give insight into the role of metacognition in cognitive performance and will foster the development of children and adolescents with ADHD in the long-term.