ADHD diagnoses increase discontinuously by a child’s school starting age, with young-for-grade students having much higher ADHD diagnostic rates. Whether these higher rates reflect over-diagnosis or under-diagnosis remains unknown. To decompose this diagnostic discrepancy, we exploit differences in parent and teacher pre-diagnostic assessments within a regression discontinuity strategy based on school starting age. We show that being young-for-grade or male generates over-assessment of symptoms…
