- Child who has a major medical condition that would interfere with involvement in the study or would be affected negatively by methylphenidate (i.e., heart disease, high blood pressure, glaucoma, untreated or unstable hyperthyroidism, uncontrolled seizure disorder, or illnesses that would require hospitalization). Children with seizures will be eligible for the study if the seizure medication is stable for 3 months and the child is seizure-free for at least 6 months;