Mark, at age 14, had more energy than most boys his age. Starting at age three, he was a human tornado, dashing around and disrupting everything in his path. At home, he darted from one activity to the next, leaving a trail of toys behind him. At meals, he upset dishes and chattered nonstop. He was reckless and impulsive, running into the street in front of oncoming cars - no matter how many times his mother explained the danger or scolded him. On the playground, he seemed no wilder than the other kids. But his tendency to overreact - like socking playmates simply for bumping into him - had already gotten him into trouble several times. His parents didn't know what to do. Mark's doting grandparents reassured them, "Boys will be boys. Don't worry; he'll grow out of it." But he didn't.
Can we differentiate Mark's hyperactivity from his impulsiveness? The DSM-V presents the symptoms of impulsivity and hyperactivity as one list. Following the suggestion of a number of researchers who had argued that a hyperactivity-impulsivity or behavioral disinhibition dimension is a better descriptor because children who show one set of behaviors typically show the other as well (Barkley, 1996; Lahey et al., 1988). This is why the term "behavioral disinhibition" (or "hyperactivity-impulsivity") is being used in the field for students such as Mark. One of the most salient characteristics of this type of student is acting without considering the consequences of those actions. We see such behavior when Mark proceeds into the street.