Being a few months older than your classmates can pay off socially for decades. A new working paper finds that boys who are among the oldest in their school cohort make more friends, win more leadership roles, and grow into men with larger networks who more often run teams or start businesses.
The study, by Matthew Jacob of Harvard University and Michael Bailey of Meta, was released as a Harvard working paper in May 2026.
Using school entry cutoffs as a natural experiment
Because school entry depends on birthdate cutoffs, children born just before and just after a cutoff end up at opposite ends of their class’s age range. The authors used a fuzzy regression discontinuity design around these cutoffs, together with data from Facebook, to estimate the causal effect of being relatively old.
More friends, more presidents, more managers
Boys who were older than their classmates made 11% more friends in high school. They were also 42% more likely to become class president than their relatively younger peers.
The advantage persisted. Men who had been relatively old as children had larger social networks as adults, and they sorted disproportionately into management and entrepreneurship.
The authors conclude that small age differences within a peer group can have lasting effects on social and economic outcomes. For parents weighing whether to hold a son back a year, the age gap inside a single classroom turns out to be measurable in friendships and careers.
Study Details:
- Title: Who Leads? Relative Age Effects on Social Capital
- Authors: Matthew Jacob, Michael Bailey
- Journal: Harvard Working Paper (SSRN)
- Publication Date: May 2026
- DOI: 10.2139/ssrn.6844065