Does the Early Bird Catch the Label? Relative Age Effects in the Assessment of Special Educational Needs and ADHD: Evidence from Germany

This study investigates the causal effect of relative age at school entry on the likelihood of being identified with special educational needs (SEN) or diagnosed with attention deficit/hyperactivity disorder (ADHD) in Germany. Drawing on representative data from the National Assessment Studies (IQB) for Grades 4 and 9, we use a two-stage least squares (2SLS) instrumental variable approach, leveraging exogenous variation in school starting age created by state-specific enrollment cutoff dates. Results indicate that relatively younger students within a grade cohort are significantly more likely to be classified with SEN, particularly in the domains of learning and developmental disorders, with effects being more pronounced in Grade 9 than in Grade 4. Similarly, we find robust evidence of a relative age effect on ADHD diagnoses in Grade 4, although this effect diminishes by Grade 9. The findings suggest that age-related maturity differences systematically influence assessment and diagnostic decisions. Our results highlight the need for developmentally sensitive and bias-mitigating assessment practices that do not rely solely on teacher judgments, in order to avoid misclassification and ensure educational equity.