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ADHD or Adolescence
Frustrated Child Being Calmed.

Attention deficit-hyperactivity disorder (ADHD) diagnoses have increased over the last two decades. Between 2007 and 2012, rates rose by a further 50%, which generated concerns from experts about an appropriate level of diagnosis. A potential contributing factor is the arbitrary age cutoff for public school entry in most U.S. states (i.e. children must be 5 years old by September 1st). As a result, students born in August, directly entering kindergarten, are almost a year younger than those born in September, who had to wait. This interacts with a unique aspect of ADHD diagnoses—reliance on teacher and parental assessments of a child compared to their same-grade peers. This is significant in kindergarten, as overly active behavior in younger students could be attributed to relative immaturity.

Understanding this issue, Anupam B. Jena, an Early Independence Awardee (2013), asked the question: Are the youngest children in a kindergarten class more often diagnosed with ADHD?

To address the query, Dr. Jena and his team scoured an insurance claims database with information on roughly 407,000 U.S. children, also providing information about ADHD and other diagnoses. They focused on students born between 2007-2009 and tracked them until 2015. They found younger “August-born” children, were diagnosed at rates approximately 34% higher than older “September-born” children (85.1 vs. 63.6 per 10,000 children, respectively). This finding also seemed to be specific to ADHD, as no differences were found in the rates of some other diseases including asthma, diabetes, or obesity. These data may suggest the children’s younger ages were playing a role in ADHD diagnosis.

While the results are informative, it is important to understand that this study does not prove students are being misdiagnosed. Another possible interpretation is that many students in September cutoff-states could be getting appropriate early diagnoses, with increased ADHD rates being caused by some currently unidentified factor. Additionally, relying only on insurance data makes it difficult to assess confounding factors, as other childhood issues appear as ADHD (e.g. medical conditions, overcrowded classrooms, or psychiatric issues). Even considering the caveats, the use of a large sample size and insurance records rather than subjective recall of subjects, lends credibility to the findings. The results may highlight shortcomings in how ADHD is identified, but more studies will be needed to understand what underlies this phenomenon.


  • Attention Deficit--Hyperactivity Disorder and Month of School Enrollment. Layton, T. J., Barnett, M. L., Hicks, T. R., & Jena, A. B. New England Journal of Medicine, (2018). 379(22), 2122-2130.

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This page last reviewed on September 13, 2023