This study examines same-sex siblings' educational mobility using high-quality register data from Norway. The study explores how the educational level of younger siblings varies with the education of parents and firstborn siblings. Younger siblings are generally more likely to attain the same education as the eldest. Even though the distance and direction of educational mobility co-varies between the eldest and younger siblings, the association appears weaker when the firstborn children of highly educated parents only attain compulsory schooling. Furthermore, educational similarity within and across generations is particularly widespread among the families with the least and most educated parents. The study demonstrates how differentials in educational attainment by family background increase when comparing sibling pairs rather than individuals. Accordingly, researchers must also consider family outcomes to understand the stratification that follows intergenerational mobility.