August-born children living in states with a school enrollment cut-off date of September 1 are 30 percent more likely to receive a diagnosis of attention-deficit/hyperactivity disorder (ADHD), compared with their slightly older peers enrolled in the same grade, according to a new study led by Harvard Medical School researchers.

The findings, published in The New England Journal of Medicine, underscore the notion that at least in a subset of elementary school students, an ADHD diagnosis may be influenced by earlier school enrollment.

In general, the rate of ADHD diagnoses among children has risen dramatically over the past two decades. In 2016 alone, more than 5 percent of U.S. children were being actively treated with medication for ADHD. Experts believe the rise is fueled by a combination of factors, including a greater recognition of the disorder, a true rise in the incidence of the condition and, in some cases, improper diagnosis.

“Our findings suggest the possibility that large numbers of kids are being over-diagnosed 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 lead author Dr. Timothy Layton, assistant professor of health care policy in the Blavatnik Institute at Harvard Medical School.

Most states have arbitrary cut-off birth dates that determine which grade a child will be placed in and when they can start school. In states with a Sept. 1 cut-off date, a child born on Aug. 31 will be nearly a full year younger on the first day of school than a classmate born on Sept. 1.

At this age, the younger child might have a harder time sitting still and concentrating for long periods of time in class, said Layton. That extra fidgeting may result in a medical referral, followed by diagnosis and treatment for ADHD.

This dynamic may be particularly true among younger children given that an 11- or 12-month difference in age could lead to significant differences in behavior, said the researchers.

For example, what might be normal behavior for a boisterous 6-year-old could seem relatively abnormal relative to the behavior of older peers in the same classroom.

“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 senior author Dr.Anupam Jena, the Ruth L. Newhouse Associate Professor of Health Care Policy in the Blavatnik Institute at Harvard Medical School and an internal medicine physician at Massachusetts General Hospital.

“A normal behavior may appear anomalous relative to the child’s peer group.”

Using a large insurance database, the research team compared the difference in ADHD diagnoses by birth month — August versus September — among more than 407,000 elementary school children born between 2007 and 2009, and who were followed until the end of 2015.

In states that use Sept. 1 as a cut-off date for school enrollment, children born in August had a 30 percent greater chance of an ADHD diagnosis than those born in September. No such difference was found among children born in August and September in states with cut-off dates other than Sept. 1 for school enrollment.

Specifically, 85 out of 100,000 students born in August were either diagnosed with or treated for ADHD, compared with 64 students per 100,000 born in September. When the researchers looked at ADHD treatment only, the difference was also large — 53 of 100,000 students born in August received ADHD medication, compared with 40 of 100,000 for those born in September.

ADHD diagnoses and treatment rates have increased dramatically over the last 20 years. In 2016 alone, more than 5 percent of all children in the United States were taking medication for ADHD, the authors note.

The reasons for the rise in ADHD incidence are complex and multifactorial, Jena said. Arbitrary cut-off dates for school enrollment are likely just one of many variables driving this phenomenon, he added.

In addition, many states have recently adopted measures that hold schools accountable for identifying ADHD and give educators incentives to refer any child with symptoms suggesting ADHD for medical evaluation.

“The diagnosis of this condition is not just related to the symptoms, it’s related to the context,” Jena said. “The relative age of the kids in class, laws and regulations, and other circumstances all come together.”

Source: Harvard Medical School