This paper examines factors possibly responsible for the poor outcomes of many children with attention deficit hyperactivity disorder (ADHD) and suggests possible ways of improving services to this population. It is concluded that each of the etiological factors identified for ADHD has its own characteristics, driven by genetic vulnerabilities and shaped by the child's life experiences. Specific ADHD is seen to involve inattention, impulsivity, and hyperactivity without any etiological implication. Specific ADHD is subdivided into two major groups, the behavioral subtype and the cognitive subtype, which respond to different forms of intervention including stimulant medication. The failure to account for heterogeneity in the ADHD population is seen to be responsible for the mixed findings of studies on the effectiveness of methylphenidate therapy. Schools are encouraged to recognize the heterogeneity of the ADHD syndrome; provide comprehensive diagnosis in cooperation with medical and other professionals; and devise individually appropriate combinations of remedial education, medication, behavioral modification, and support. (31 references)