According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), there are actually three different types of attention deficit hyperactivity disorder:
Predominately inattentive type: Often referred to as attention deficit disorder, or ADD, this sub-type involves impaired attention and concentration, as well as "daydreamy" behavior. These children are not overly active and do not disrupt classrooms; instead, they typically fail to complete tasks, are easily distracted, make careless errors, and avoid activities that require sustained mental work and close concentration. Because they are not disruptive, their symptoms are more likely to be overlooked. These children are often misread as being lazy, unmotivated, and irresponsible. This accounts for approximately 30% of individuals with ADHD.
Predominately hyperactive-impulsive type: Children are both hyperactive and impulsive but usually do not have problems paying attention. This accounts for approximately 10-20% of individuals with ADHD.
Combined type: The most common type involves all ADHD symptoms, including inattention, distractibility, hyperactivity, and impulsivity. This accounts for approximately 50-60% of individuals with ADHD.