The purpose of this study was to examine the effect of a family-centered intervention delivered during early elementary school, the Family Check-Up (FCU), in supporting parents' use of proactive parenting skills and the role that parental self-efficacy has in promoting proactive parenting. We predicted both direct and mediated effects of the FCU on changes in proactive parenting. Participants were the primary caregivers of 321 kindergarten children and randomly assigned to either the FCU or to a school-as-usual control group (n = 164 assigned to intervention). Results indicated that the FCU initiated during kindergarten enhanced proactive parenting skills directly and was mediated by parental self-efficacy. These results highlight the FCU as an efficacious intervention in early elementary school in promoting proactive parenting skills and parental self-efficacy and underscore the role of parental self-efficacy as a primary pathway towards improved proactive parenting. [This paper was published in "Journal of Family Psychology" v37 n3 p380-387 2023.]