Birth order and educational attainment: evidence from fully adopted sibling groups

This study uses data on fully adopted sibling groups to test whether the explanation for the consistently observed negative effects of birth order are physiological or social in origin. Swedish administrative register data is used to construct full sibling data for cohorts born 1960–1982. Using a within-family comparison approach, I compare adopted siblings of different adopted birth order to one another to see whether birth order amongst adopted children (N = 6968) is associated with educational attainment by age 30, and the likelihood of having entered tertiary education by age 30. These same within-family comparison analyses are also performed on siblings in fully biologically related sibling groups (N = 1,588,401). I find that there is a negative relationship between adopted birth order and both educational attainment and the likelihood of entering tertiary education in fully adopted sibling sets. These findings strongly suggest that differences in educational attainment by birth order are driven by intrafamily social dynamics. I also conduct additional analyses in fully adopted sibling groups where age order and adoption order are reversed to test whether there is evidence for tutoring by siblings. These results do not indicate clear support for any tutoring effect.