Children with many siblings have lower average educational attainment compared with children raised in smaller families, and this disadvantage by sibship size has been observed across many countries. We still know remarkably little, however, about how sibship size disadvantage has changed within countries and how such trends vary across countries. Using comparative data from 111 surveys from 26 low-fertility countries, we find an overall trend of growing sibship size disadvantage across cohorts in the majority of countries: between the 1931-1940 birth cohort and the 1971-1980 birth cohort, 16 of 26 countries showed a statistically significant increase in sibship size disadvantage in education, while only two countries showed a significant reduction in sibship size disadvantage. The disadvantage in years of education associated with having an additional sibling increased remarkably in post-socialist (0.3) and East Asian countries (0.34) and, to a lesser extent, Western European countries (0.2). In contrast, this disadvantage showed little change in Nordic countries (0.05) and even decreased in Anglo-Saxon countries (-0.11). We discuss explanations and implications of our comparative evidence in the context of the intergenerational transmission of education.

Children with many siblings have lower average educational attainment compared to children raised in smaller families. This disadvantage by sibship size has been observed across many different countries. We know remarkable little, however, about how sibship size disadvantage has changed over time within countries and how such trends vary between countries. Using comparative data from 114 surveys from 26 low-fertility countries, we find an increase of the sibsize disadvantage over time in the majority of countries: between the 1931-40 birth cohort and the 1971-80 birth cohort, 16 out of 26 countries showed a statistically significant increase in the sibship size disadvantage in education, while only two countries -Australia and the UKshowed a statistically measurable reduction in the sibship size disadvantage. In many countries, growing differential fertility by parental education played a substantial role in the increasing disadvantage. We discuss possible explanations and implications of the increased disadvantages and the variation in trends and levels between regions and specific countries.