 Participation in the study will last between 5 and 6 months. All eligible participants will begin treatment with stimulant medications for 2 to 6 weeks, or until an optimal medication dosage has been determined. During this medication dosing phase, study staff will collect weekly ratings of the child participants behavior at home and school, and participants will be seen weekly by study doctors to monitor medication dosage. Upon achieving an optimal dose, child participants will answer questions about their mood and behavior. 