Little is known about the role birth order plays in delinquency and adult crime outcomes that carry significant externalities. We use rich data sets from Denmark and Florida to examine these outcomes and explore potential mechanisms. Despite large environmental differences between the areas, we find remarkably consistent results: in families with two or more children, secondborn boys are 20%–40% more likely to be disciplined in school and enter the criminal justice system than are their firstborn male siblings. We rule out health at birth and school quality as mechanisms but find evidence for the role of parental time investment.

Recent evidence indicates that boys and girls are differently affected by the quantity and quality of family inputs received in childhood. We assess whether this is also true for schooling inputs. Using matched Florida birth and school administrative records, we estimate the causal effect of school quality on the gender gap in educational outcomes by contrasting opposite-sex siblings who attend the same sets of schools--thereby purging family heterogeneity--and leveraging within-family variation in school quality arising from family moves. Investigating middle school test scores, absences and suspensions, we find that boys benefit more than girls from cumulative exposure to higher quality schools.