Attention-deficit hyperactivity disorder (ADHD), consists of a persistent pattern of abnormally high level of activity, impulsivity, and/or inattention that is more frequently displayed and more severe than is typically observed in individuals with comparable levels of development. The pattern of behavior usually arises between the ages of 3 and 5, and is diagnosed during the elementary school years due to the child's excessive locomotor activity, poor attention, and/or impulsive behavior. Most symptoms improve during adolescence or adulthood, but the disorder can persist or present in adults. It has been estimated that 3-7 percent of school-age children have ADHD.