The Research-based Developmentally Informed (REDI) program enriched Head Start classrooms with teacher-delivered curriculum components designed to enhance child social-emotional learning and language-literacy skills. Parents received information about the program via backpack express, including weekly handouts about program topics and three DVDs illustrating REDI interactive strategies and suggesting home learning activities. In addition to effects on child skill acquisition and school performance (reported previously), positive effects emerged on a family-based outcome: parents of children in REDI-enriched classrooms reported higher quality preschool parent-child conversations than parents in the randomized control group (usual practice) classrooms. This study examined the long-term benefits associated with intervention-related improvements in preschool conversations. The original sample included 356 children (58% White, 24% Black, and 18% Latinx; 54% girls, 46% boys); 77% had the high school follow-up data used in this study. Longitudinal GLM analyses documented significant REDI intervention effects on parent-adolescent communication quality (assessed in the 7th and 9th grades) and on parent- and youth-reported high school behavior problems (assessed in 11th grade). Path analyses revealed significant serial mediation from intervention-related improvements in preschool conversations to parent-adolescent communication quality (grades 7-9) to reductions in later youth-reported (but not parent-reported) behavior problems (grade 11). The findings suggest that including "light touch" parent engagement materials with preschool classroom interventions can contribute to long-term program benefits.