An 8-year-old boy is brought to the child psychiatry clinic by his mother with complaints of inattention, hyperactivity, and impulsivity at school for the past 18 months. The teacher reports difficulty in following instructions and frequent disruption of class. On clinical interview, the child meets DSM-5 criteria for ADHD, combined presentation. The mother denies any significant past medical or psychiatric history. Physical examination and basic investigations are normal. What is the most appropriate next step in management?