<qa>  What is the main phase of treatment?The study will be a double-blind placebo-controlled trial of risperidone as an augmenting agent in 40 children, 7-12 years of age, with ADHD. All subjects would have been treated first with a stimulant medication as a single agent, but continue to present impulsive aggression. The active phase of treatment will be four weeks long, during which risperidone or placebo will be added to a constant dose of stimulant medication. The study will include a four weeks continuation phase where placebo nonresponders will have the opportunity to receive risperidone on an open basis. 