A comprehensive model of family influences on educational resemblance of siblings expands the traditional sibling pair model to a full sibship model in order to investigate how gender, gender composition of sibships, and a measure of ordinal position moderate the effect of social origins on educational attainments of siblings. One common family factor is sufficient to explain the variation of educational attainment among brothers and sisters. Although effects of social origins variables on brothers are larger than on sisters, the relative effects of measured social origins are virtually the same among sisters and brothers. The disparity between educational attainments of brothers and sisters persists across sex composition and family size. Ordinal position does not alter the effects of social origins on educational attainment nor does it directly affect educational attainment. Father's and mother's education are equally important for all siblings regardless of birth order, gender composition, and family size.