Sibling set order and educational attainment: evidence from fully adopted sibling groups

Kieron Barclay, Stockholm University

There is an extensive theoretical and empirical literature concerning the relationship between birth order and educational attainment and cognitive development. Most of these theories postulate that differences in educational attainment by birth order stem from intrafamily social dynamics, but there are also hypotheses that suggest that these differences may have biological underpinnings. This study uses Swedish administrative register data to construct full sibling data for cohorts born 1960 to 1977 for fully adopted siblings sets. Using a within-family comparison approach, I compare adopted siblings of different set order to one another to see whether set order amongst adopted children is associated with differences in 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 sets to serve as a comparison to the analyses of adopted children. I find that there is a negative relationship between set order and both educational attainment and the likelihood of entering tertiary education in fully adopted sibling sets, which is slightly stronger than that seen in fully biologically related sibling sets. These findings strongly suggest that differences in educational attainment by set order are driven by intrafamily social dynamics.