ABSTRACT. Objective: This study reports effects of a parenting program to increase parents' readiness to socialize their children against early alcohol use. Method: A two-group randomized controlled trial was conducted with a nonprobability sample of 816 mothers. Participants were recruited from school districts located primarily in North Carolina and completed telephone interviews at baseline and 6 and 18 months after delivery of a parenting program to the treatment group mothers. Mothers reported on psychological indicators of readiness to prevent child alcohol use (e.g., attitude toward child sipping) and on parenting behaviors with potential to prevent such use (e.g., setting rules about child sipping). Multivariate analysis of variance models tested program effects on composite sets of psychological and behavioral outcomes; step-down analysis identified the individual outcomes driving overall program effects. established beliefs about the consequences of child sipping, educational attainment, and race/ethnicity was tested. Results: The program had significant overall effects on each composite set of psychological and behavioral outcomes. Effects on psychological outcomes were moderated by mother's alcohol use, beliefs about the consequences of child sipping, and educational attainment; effects on the behavioral outcomes were moderated by mother's race/ethnicity. Conclusions: The parenting program had favorable, sustained effects on targeted outcomes intended to increase parental readiness to socialize children against early alcohol use. Mothers expected to be least receptive to the program-those who, at baseline, believed that allowing children to sip alcohol can have beneficial consequences-were most changed by it. (J. Stud. Alcohol Drugs, 77, 327-336, 2016)