Studies in social stratification have used siblings as a tool to learn about the intergenerational transmission of advantage but less often have asked how siblings impact one another’s life chances. The author draws on social capital theory and hypothesizes that when youths attend college, they increase the probability that their siblings attend college. The author further hypothesizes that this effect is strongest among youths whose parents do not have college degrees. Findings from a U.S. national probability sample support both hypotheses. Although it is possible that confounding factors drive the estimates, the author conducts robustness checks that show that confounding would need to be very atypically strong to invalidate a causal interpretation. The positive main effect suggests that an intragenerational transmission of educational advantage exists alongside the intergenerational transmission that receives more attention. Effect heterogeneity points to the potential redundancy of college-educated siblings’ benefits when youths already receive similar benefits from college-educated parents.