This study examines how sibship characteristics affect educational attainment in Taiwan. Using a multilevel analysis of a sibling sample of 12,715 observations from 3,001 families drawn from a national survey, we investigate the effects of family size, sibship density, birth-order rank, and sibship gender composition. The results support the argument that the effect of son preference on intrafamily educational inequality is conditional on family resources. We also find, however, that male firstborns, who are the ultimate inheritors of paternal authority in Chinese families, have additional leverage in the sibling competition for family resources. The privilege for firstborns does not extend to daughters. Therefore, we argue that culturally defined norms regarding seniority and gender help shape intrafamily resource allocation in Chinese society.