Disorder characterized by attentional deficit and/or hyperactivity—impulsivity more severe than expected for a developmental age.

Attention Deficit/Hyperactivity Disorder (ADHD), which affects 3-5% of school-age children in the United States, refers to a combination of excessive motor restlessness, difficulty in controlling or maintaining attention to relevant events, and impulsive responding that is not adaptive.

For some children hyperactivity is the primary feature of their ADHD diagnosis. These children may be unable to sit quietly in class. They may fidget in their chairs, sharpen their pencils multiple times, flip the corners of the pages back and forth, or talk to a neighbor. On the way up to the teacher's desk they may take several detours.

Most children with ADHD have both attentional and hyperactivity-impulsivity components, and so they may experience difficulties regulating both attention and activity. Although many children who do...