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A new study suggests that children who must turn 5 years old by Sept. 1 in order to start kindergarten that year — or children born in August — are more likely to receive a diagnosis of attention deficit hyperactivity disorder.

SALT LAKE CITY — A new study suggests that in states where children who must turn 5 years old by Sept. 1 in order to start kindergarten that year, children born in August, are more likely to receive an ADHD diagnosis.

What’s going on: Researchers in the new study found that there were more diagnoses among children born in August, specifically in states where there is a Sept. 1 cutoff date to start kindergarten, CNN reports.

  • These August-born children would then be the youngest in their classes, the study notes.
  • "We saw nothing for any of the pairs of months apart from August to September, where we saw this big difference," said Timothy Layton, an assistant professor of health care policy at Harvard Medical School, who was the lead author on the study. "We saw that this was only in states that had a Sept. 1 cutoff. There was nothing in states that didn't have that."

Why it matters: "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," Layton said, according to Science Daily.

Method: The study looked at more than 407,000 U.S. children born from 2007 to 2009. Researchers tracked the diagnoses through an insurance database.

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Specifics: The rate for ADHD diagnoses was 34 percent higher for those with August birthdays compared to those with September birthdays, CNN reports.

States: The study found there are 21 states with the cutoff date, including Arizona, Texas and Illinois, among several others, according to the Education Commission of the States.

Other states have different enrollment dates, including Dec. 2 in California and Jan. 1 for Vermont.

The report lists Utah's cutoff date as Sept. 2.

Bigger picture: Physicians should be made aware of these findings to help them avoid overdiagnosis, the researchers wrote for The New York Times.