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Children With August Birthdays Are More Likely to Be Misdiagnosed With ADHD

Enrollment cut-off dates could be why some kids with ADHD diagnoses need more time to grow up.


Children with August birthdays are more likely to be diagnosed with ADHD, a new study confirms—assuming, that is, they live in states with an enrollment cut-off in September. Indeed, scientists have long known that September-born kids in many states experience significant academic and athletic advantages, due to arbitrary enrollment cutoff dates that render them most mature in the classroom. However, the new research highlights the downside of September enrollment cut-offs: August babies are often left behind.  

“Our findings suggest the possibility that large numbers of kids are being overdiagnosed and overtreated for ADHD because they happen to be relatively immature compared to their older classmates in the early years of elementary school,” said study coauthor Timothy Layton of Harvard Medical School, in a statement.

The number of children diagnosed with ADHD has steadily increased over the past decade, according to the Centers for Disease Control and Prevention. Experts have attributed this rise to greater recognition of the disorder, but also to an increase in misdiagnoses. One study published in the Journal of Pediatrics analyzed ADHD diagnosis data from 378,881 Taiwanese children (Taiwan’s has an August 31st cut-off date, like most American school districts). They found that children with August birthdays were significantly more likely to be diagnosed with ADHD.

To see how this played out in the U.S., Layton and colleagues looked at the records of 407,000 of children born between 2007 and 2009, who were tracked until the end of 2015. Children born in August in states with a September 1 cut-off date had a 30 percent greater chance of receiving an ADHD diagnosis. Interestingly, no such differences were seen in states that did not have September 1 cut-off dates. The trend held when it came to children taking medications for ADHD. Fifty-three out of every 10,000 children born in August were medicated for ADHD, to September’s 40 out of 10,000.

“As children grow older, small differences in age equalize and dissipate over time but, behaviorally speaking, the difference between a 6-year-old and a 7-year-old could be quite pronounced,” said study coauthor Anupam Jena, also of Harvard Medical.

Layton and Jena are careful to note that the reasons for the rise in ADHD diagnoses are multifactorial, and enrollment cut-off dates probably only account for a small portion of the increase. Still, the crucial takeaway for parents, pediatricians, and teachers is that it might be important to consider immaturity before jumping to a diagnosis.

“The diagnosis of this condition is not just related to the symptoms, it’s related to the context,” Jena adds. “A child’s age relative to his or her peers in the same grade should be taken into consideration and the reasons for referral carefully examined.”