The objective of this study was to evaluate the effect of a family-centered preventive intervention, the Family Check-Up (FCU), on improving parenting skills during kindergarten and 1st grade, when children are challenged to engage in a variety of new behaviors, such as sustained attention and self-regulation of behavior in the classroom. Building on prior research and funded by the Department of Education, we tested the effect of the FCU on parenting skills during the transition to kindergarten. We predicted both direct and moderated effects of the FCU on changes in parenting, including positive parenting, monitoring/family routines, and negative parenting skills. In this registered clinical trial (NCT02289092; see CONSORT diagram in Figure 1), participants were 321 families of kindergarten children recruited from 5 public elementary schools and randomly assigned to either the FCU or to a school-as-usual control group (n = 164 assigned to intervention). Families engaged in the intervention at a high rate (75%) and completed assessments about parenting skills from kindergarten to 1st grade. Results suggest that FCU effects on parenting skills were moderated by parenting contextual stress. As stress increased, so did positive effects of FCU on monitoring/family routines and negative parenting. No effects on positive parenting skills were observed. Results of this research suggest the effects of the FCU are more pronounced for high-stress families and contribute to the literature supporting adaptive, tailored approaches to intervention for high-risk children and their caregivers. [This paper will be published in "Journal of Family Psychology" v34 n1 p122-127 2020.]