Background: Prior work reports a relative age effect (RAE), in which children are more likely to be diagnosed with Attention-Deficit/Hyperactivity Disorder (ADHD) if they are relatively younger than their classmates. Yet work reporting a RAE in ADHD diagnosis has analyzed relatively dated samples, has not examined moderation across sociodemographic characteristics, and has largely not examined the RAE in longitudinal analyses. We examined whether entering kindergarten as a relatively younger student increased the likelihood being diagnosed with ADHD across elementary school. We also examined moderation by race and ethnicity, biological sex, socioeconomic status, and home language. Methods: We analyzed data from the Early Childhood Longitudinal Study–Kindergarten Cohort (ECLS-K: 2011; N = 11,410), a nationally representative cohort. Logistic regression models estimated relations between children’s relative age and both grade-specific and cumulative ADHD diagnoses during elementary school. Discrete-time event history logit regression models examined the timing of ADHD diagnosis from kindergarten through fifth grade. Interaction terms assessed moderation by sociodemographic characteristics. Results: We generally failed to observe evidence of a RAE, either cumulatively or within specific grades. Discrete-time event models indicated no significant relations between relative age and timing of ADHD diagnosis. Moderation analyses identified isolated interactions, indicating the possibility of a specific RAE for Black children and those from non-English-speaking homes in select grades. However, these predicted effects were not consistently observed and did not survive correction for multiple comparisons. Conclusions: In contrast to prior work analyzing older datasets, we failed to observe a RAE in U.S. elementary schools. Our finding suggest that relatively younger children attending U.S. elementary schools are not at increased likelihood for ADHD diagnosis.
Hu et al. (Tue,) studied this question.