- Phase 2: titration (week 2 - 5) If the screening indicates that the child is eligible and the parents would like to start a medication treatment for their child, they can participate in a 4-week open-label titration of LDX. The aim of this stepwise titration procedure is to determine the child's clinically most effective dose. LDX will be started at a dose of 30mg/day and adjusted up to 70 mg/day if necessary. During the titration phase the parents will be asked to fill in a daily diary. Before the medication trial and at the end of each week of the medication trial, the investigators will measure symptom change and evaluate potential side effects of LDX. These assessments will include monitoring ADHD symptoms and physical examination for potential drug side effects. Furthermore, the physician will monitor weight, length, blood pressure and heart rate during each visit.