Abstract
In the course of a prospective longitudinal study, we examined age of onset of behavior problems in a group of boys and girls identified with attention deficit disorder (ADD) at age 11. Onset occurred during the preschool years, by the first year of schooling, or by the end of the second year of school. Onset was strongly related to informant source at age 11, pattern of comorbidity of disorder at age 11, and developmental language, perceptual motor, and IQ measures. Onset by the first year of schooling was particularly related to poor reading skills. By age 15, nearly three-quarters of those with onset of problems before age 6 had one or more DSM-III disorders.