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Kindergartners Born in August More Likely to Be Diagnosed with ADHD

A new study published by The New England Journal of Medicine finds that the immaturity of younger students whose birthdays fall close to enrollment cut-offs may be mistaken for attention deficit disorder.



November 30, 2018

Most U.S. school children start kindergarten at age five; the birthday cutoff in 34 states is on or before September 1. In states like Virginia, Maine, or Connecticut, a kindergarten student may not turn 5 until months into the school year — some as late as December 31. This raises a complicated issue for parents of late Summer and, in some cases, Fall babies: Should I enroll my child now, knowing she’ll be the youngest in her class, or wait a year?

A child born on August 31 or September 2, for example, could vary in age from his same-grade classmates by nearly one year – causing real developmental and maturity differences between students in the classroom, particularly in early grades.

A new study1, published in The New England Journal of Medicine, examined the impact of this variance on ADHD diagnoses. The researchers analyzed insurance database statistics for 407,846 children born between 2007 and 2009, that followed the subjects through 2015. They compared the rate of ADHD diagnoses among children with birthdays close to their states’ enrollment cutoff dates.

The result was clear: In states with a September 1 birthday cutoff for kindergarten registration, the youngest children in the class – those born in August – were more likely to be diagnosed with and treated for attention deficit disorder (ADHD or ADD) than were their peers born in September. This finding is echoed in previous studies from around the world.

In the study, 85.1 per 10,000 children born in August had ADHD diagnoses. Only 63.6 per 10,000 children born in September had ADHD diagnoses. 52.9 per 10,000 children born in August were treated for ADHD. Only 40.4 per 10,000 children born in September were treated.

This difference was not observed in states without September 1 enrollment cutoff dates, leaving clinicians to wonder: Are age-based behavior variances being mistaken for ADHD? Could it be that behaviors often flagged as symptoms – difficulty paying attention, sitting still, or controlling impulses – are the natural differences between a 5-year-old child and his 6-year-old classmate?


1Timothy J. Layton, Ph.D.; Michael L. Barnett, M.D.; et al. “Attention Deficit–Hyperactivity Disorder and Month of School Enrollment.” The New England Journal of Medicine. 2018; 379:2122-2130. doi: 10.1056/NEJMoa1806828

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