This study investigates how characteristics of young mothers, their childrearing environments, and their participation in a paraprofessional home visiting program for young parents determine the program's impact on parenting, including child maltreatment. It is intended to contribute to the general literature on home visiting effectiveness, and to shed particular light on individual and contextual characteristics that moderate program effects. Findings should also advance policymakers' and practitioners' efforts to maximize the impact of home visitation as a strategy to prevent child maltreatment. (author abstract)