Prior research points to the promotion of parenting self-efficacy (PSE) as an important component of parenting interventions; however, few studies have tested PSE as a mediator or moderator of the effects of parenting programs on child behavior. In the current study, we examined the efficacy of the Family Check-Up (FCU), a brief, strengths-based parenting intervention, adapted for kindergarten school entry. We tested the FCU's effects on reducing growth in parent-reported child conduct problems (CP) from kindergarten to 5th grade, and whether PSE functioned as a mediator or moderator of intervention effects, using a latent growth curve model and intent-to-treat approach. Participants were parents of 321 children from five elementary schools in a Northwestern United States city. Although we did not find a main effect of the FCU in reducing growth in CP from kindergarten through 5th grade, we found a significant indirect effect of the FCU on reducing CP growth via improving PSE in 2nd grade, and that the indirect effect was moderated by baseline levels of PSE. Together, our findings suggest the FCU is effective in promoting PSE, which is subsequently associated with reduced CP growth, particularly for parents with initially low PSE. Our findings bolster existing work on the relationship between PSE and child CP in the context of a preventive parenting intervention and emphasize the importance of PSE as an agent of change. [This paper was published in "Journal of Family Psychology."]