Objective: Increasingly, social workers are using standardized skill-building models to provide services to children that are time limited, focused on specific attainable goals, and easily evaluated. Scant attention has been paid to the impact of leader and group factors on the behavioral change of participants in skill-building groups. Method: Multiple regression analysis was used to determine the effects of leader education and experience, therapeutic alliance, and group participation on the prosocial skill development of low-income, elementary-aged children at risk for aggressive behavior. A total of 794 children participated in 106 groups led by 24 graduate/non-graduate-level leaders. Results: Findings indicated that development of prosocial skills decreased aggressive behaviors in the groups. Education level of the leader and group participation contributed to skill development. Experience level implementing the intervention affected aggression level. Conclusions: The findings have important implications for training and supervision of group facilitators, future research on skill-based groups with children, and generalization of skills to school, family, and community settings.