All subjects will be screened for eligibility inclusion and exclusion criteria. All concurrent non-pharmacological therapies will be stabilized for a minimum period of 2 weeks prior to the child's entry into the drug phase of the study. At each medication follow-up visit, a detailed history will be obtained and recorded for all concurrent treatments. If a child enrolls in this study, his/her participation will last approximately 3 to 4½ months with 12-18 outpatient daytime visits.