Parents, children and experimenters will be blind to treatment conditions. For blinding purpose we will blindfold the children when taking IMP or placebo (e.g. LDX and placebo capsules are not completely identical; however, the difference is barely noticeable when one is blindfolded). The order of the treatment conditions (LDX vs. placebo) will be randomly assigned and counterbalanced across children. Between the treatment conditions there will be an interval of approximately 1 week. During these intervals LDX intake will be continued. Before each testing session there will be a washout period of at least 48 hours; the LDX or placebo is given the morning of the testing. Each testing session will take place at the same time of day; preferably in the afternoon to minimalize possible time of day effects and approximately 3-4 hours after the child took LDX or placebo.