This article analyses the pattern of inequality across levels of education and its evolution over time from a cross-national comparative perspective. We employ a previously disregarded approach of sibling correlations to measure how the contribution of the total family background differs across achieved levels of education. We compare successive birth cohorts in Finland, Sweden, Germany, and the U.S. between 1990 and 2015. We further analyze the extent to which the total contribution of parental background is accounted for by observed parental education. Our results indicate a pattern in which sibling similarity is strongest in the lowest and the highest levels of education in all studied countries. Changes over time were more pronounced in the Nordics and in educational levels other than the lowest. Observed parental education played a less notable role than expected, indicating that using only parental education ignores a substantial portion of the total influence of family background.