As postsecondary education is an increasingly important developmental milestone for adolescents, it is critical to identify supports that help prepare youth for college. Building on evidence highlighting the role of parental input and guidance, the current study investigates how within-person changes in adolescent school-related communication (i.e., frequency of talking about school and educational planning) with friends and family across high school contribute to college preparedness and subsequent enrollment. Capitalizing on a diverse adolescent sample (N = 4,495), longitudinal analyses across high school showed that school-related communication with friends increased, but remained relatively stable with family, from Grades 9-12 (approximately ages 15-18 years). Parallel process latent growth curve modeling demonstrated that steeper increases in school-related communication with friends independently predicted college enrollment, consistently across racial/ethnic and parental education groups. Moreover, within-person changes in friend and family school-related communication across high school interacted in a compensatory fashion to predict grade point average and perceived college readiness at 12th grade. At a time of growing need for independence from parents, the findings highlight the positive developmental function of friends in helping adolescents reach a critical educational milestone.