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.
Goldan et al. (Mon,) studied this question.