When a health care professional tells a parent that they suspect a child has AD/HD, the diagnosis is based upon the child's having met a certain list of noticeable symptoms with a certain degree of frequency.  These symptoms must be seen continually over a period of six months or more in order to be considered frequent.  In addition to this, there are three types of AD/HD.  These types are differentiated by the characteristic of their AD/HD that is most prominent--inattentativeness, impulsive behavior, or hyperactivity.