Drawing on sibling data from Denmark and Florida, the research found that second-born boys are 20% to 40% more likely to face disciplinary action in school and have higher rates of contact with the criminal justice system.
The study suggests that the disparity may stem from differences in parental attention and role modeling. Firstborn children typically receive more direct supervision and adult guidance, while second-borns often grow up in an environment where parental focus is divided and older siblings—who may not yet be mature role models—exert greater influence.
The findings shed light on the subtle dynamics of birth order and their potential long-term effects on child development.