"Too Much Too Young: Relative Age and Adolescent Risky Behaviours"

Does classroom age composition affect risky behaviours? We use data from the “Health Behaviour in School Aged Children” international survey to answer this question. We explore a comprehensive set of outcomes representing risky behaviours of different type and adopt an IV strategy that leverages cross-country variations in cut-off dates for school eligibility to cope with the endogeneity of both relative and absolute age. We find that relatively younger students are more likely to smoke, use substances, and drink alcohol. Finally, we show that self-concept is the most important indirect channel through which relative age operates on risky health behaviors. These results highlight possible unintended consequences of students grouping policies.