First Step to Success is a multicomponent behavioral program for at-risk children who show signs of antisocial behavior at the point of school entry. The program incorporates behavioral intervention techniques, including praise and feedback, positive reinforcement, social skills training, teacher and parent collaboration, and time-out/response cost. First Step to Success also incorporates techniques to encourage adaptive behavior across the school day and in the home, such as sequential application of the program across the school day, delayed reinforcement at home for school performance, and parent education. This study employed a multiple baseline design across participants to evaluate previous research findings on the program. All children improved on measures of problem behavior, academic engaged time, and teacher ratings of behavioral adjustment. The authors extended prior research by assessing the collateral effects of the program on classroom peer and teacher behavior. Positive changes were found for both peer and teacher behavior. (Contains 3 tables and 2 figures.)