This policy brief describes attention deficit hyperactivity disorder (ADHD) as involving three characteristics: inattention, impulsivity, and hyperactivity. The brief reviews the causes of ADHD, including the belief that it is primarily an inherited, neurobiological disorder. The effects of ADHD on children are discussed and may include: other learning, behavioral, emotional, and developmental problems; memory and organizational problems; poor self-esteem and poor social adjustment; and school failure. The diagnosis of ADHD is reviewed, including observed neurobiological differences in individuals with ADHD. The multiple methods used to diagnose ADHD are described, including: (1) interviews with the parents and child; (2) direct observation in various settings; (3) a battery of achievement and psychometric tests; and (4) feedback from parents, teachers, and others about the child's behavior. The brief addresses how ADHD is treated and the determination that a multimodal approach is best. Recommendations for schools include: procedures for identifying a student with ADHD should allow enough time to gather adequate information; modifications and accommodations should be made to assist students with ADHD; and interventions need to be proactive and focus on the prevention of negative behavior. (Contains 39 references.) (CR)