During phase 2, they will be randomized to one of two treatment arms for eight weeks. The first treatment arm, the "simple treatment" arm, will consist of parent training plus continued treatment with a stimulant that is tolerated but has not yet decreased ADHD symptoms enough to meet our criterion of response, plus a placebo matching aripiprazole. The second treatment arm, called the "combination" arm, will consist of parent training plus continued treatment on stimulant plus augmentation with a second generation antipsychotic (aripiprazole). Aripiprazole (Abilify™ ) is a product that is FDA-approved and marketed for the treatment of schizophrenia and for the treatment of acute manic episodes associated with Bipolar I Disorder in adults only. However, aripiprazole is also used to treat children and adolescents with aggressive and oppositional disorders in standard clinical practice. We will continue randomizing patients until we have 40 children with ADHD become eligible to enter Phase 2.