If a child enrolls in this study, his/her participation will last approximately 7 to 13 weeks with a minimum of 7 outpatient daytime visits. The visits will be weekly in the beginning and then every other week once the child is taking an optimum dose of atomoxetine. Visits will take 1-5 hours each and will take place at the Department of Psychiatry in the Arizona Health Sciences Center (Tucson). The study consists of 2 periods.