Causal Mechanisms of Relative Age Effects on Adolescent Risky Behaviours

October 2025

Age differences between classmates are attracting growing attention in academic research and public policy, yet their underlying mechanisms remain understudied. We examine how relative age affects adolescents’ risky behaviors across Europe. Using Health Behaviour in School-Aged Children (HBSC) survey data and a two-stage least squares (2SLS) strategy, we provide causal estimates that isolate relative age effects from absolute age and season-of-birth confounders. Relatively younger students are significantly more likely to engage in behaviors such as substance use. To explore mechanisms, we apply two approaches. First, a novel use of causal mediation analysis à la Dippel et al. (2022) shows that academic self-concept, well-being, self-esteem, and peer support serve as amplifying channels for these effects. Differently, effects on sexual and aggressive behaviors seems to be mostly driven by maturity differences. Second, reduced-form analyses using data from a connected survey (i.e., the European School Survey Project on Alcohol and Other Drugs (ESPAD)) suggest that younger students perceive lower risks and higher peer prevalence of substance use. These findings reveal psychological and perceptual pathways through which relative age influences adolescent behavior.

Keywords

Relative age; age effects; enrollment cutoffs; risky behaviors

Education level

K-12 Education

Topics

Student Well-Being