According to the DSM-IV (Diagnostic Statistical Manual - IV), there are three sub-types of ADHD.
Predominantly Inattentive Subtype: This subtype is diagnosed if symptoms of inattention have persisted for at least 6 months and are age inappropriate. The inattentive ADHD child may fail to give close attention to details or may make careless mistakes. The child may have difficulty sustaining attention in tasks or play activities, and may not seem to listen when spoken to directly. Often the child may not follow through on instructions and may fail to finish schoolwork and chores, and may have difficulties organizing tasks and activities. The child may be forgetful and often lose things necessary for school assignments, pencils, books and school jumpers. There may be a reluctance to engage in tasks that require sustained mental effort. Hence there may be considerable arguments and excuses to avoid schoolwork or homework.
Predominantly Hyperactive-Impulsive Subtype: This subtype is diagnosed if there are some symptoms of hyperactivity-impulsivity along with fewer symptoms of inattention.
Hyperactivity symptoms: These include frequent fidgetiness with hands or feet or squirming particularly when required to sit still. There is likely to be difficulties playing or engaging in leisure activities quietly, and the child may seem to be constantly on the go, or may talk excessively. Often the child will leave his/her seat in the classroom or in other situations in which remaining seated is expected. There may be excessive inappropriate running and climbing. As the child grows into adolescence or adulthood, this may subside and feelings of restlessness may remain.
Impulsivity symptoms: The impulsive child often blurts out answers before questions have been completed, and has difficulties awaiting his/her turn. Consequently there may be frequent inappropriate interruptions, intrusions into games or butting into conversations.
Combined Subtype: When both symptom of inattention and hyperactivity-impulsivity are present, the child may be diagnosed as having the Combined Type of ADHD.