Attention Deficit Hyperactivity Disorder (also known as ADHD) is behavioral disorder that often occurs in children. It is one of the most common childhood behavioral disorders. However, attention deficit hyperactivity disorder can also occur in teenagers and adults. With attention deficit hyperactivity disorder, it is very hard for a person to concentrate, control their impulses, and act in a calm manner. Even though it is most common among children, attention deficit hyperactivity disorder is often not diagnosed until adolescence or adulthood.