 Attention deficit hyperactivity disorder ( ADHD ) is a mental disorder of the neurodevelopmental type . It is characterized by problems paying attention , excessive activity , or difficulty controlling behavior which is not appropriate for a person 's age . These symptoms begin by age six to twelve , are present for more than six months , and cause problems in at least two settings ( such as school , home , or recreational activities ) . In children , problems paying attention may result in poor school performance . Although it causes impairment , particularly in modern society , many children have a good attention span for tasks they find interesting . 
