Today, one in eight American children is diagnosed with attention deficit hyperactivity disorder (ADHD). In 1987, when ADHD made its debut in the American PsychiatricAssociation’s diagnostic manual (DSM-III-R), the authors estimated that only 1 in 33 children had the condition. This number included children with known central nervous system disorders like cerebral palsy, encephalitis, and epilepsy—diseases that were known to cause hyperactivity in children. Before …