Causal Mechanisms of Relative Age Effects on Adolescent Risky Behaviours

Age differences between class mates are attracting growing attention in academic research and public policy,yet their underlying mechanisms remain understudied. We examin ehow 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 `ala Dippeletal (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 Projecton Alcohol and Other Drugs (ESPA)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.