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Youngest kids in class are more likely to be diagnosed with ADHD than oldest kids, study finds

Children on either side of a school enrollment cutoff had different rates of ADHD diagnosis.
Children on either side of a school enrollment cutoff had different rates of ADHD diagnosis. (Sait Serkan Gurbuz for The Washington Post)
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Do some children diagnosed with attention-deficit/hyperactivity disorder really have the condition — or are they just young for their grade?

That is the provocative question posed by a new study looking at states with a strict Sept. 1 birth-date cutoff for school enrollment. Researchers found the youngest children in a grade — those born in August, just before the cutoff — were significantly more likely to be diagnosed with ADHD compared with those who were born the next month and became the oldest in their class.

“There’s no reason an August child and September child separated by just a couple weeks at birth would be any different. And yet, we found a big difference in diagnosis,” said Harvard Medical School’s Anupam Jena, one of the authors of the study published Wednesday in the New England Journal of Medicine.

The new analysis is likely to fuel the debate about whether there is an epidemic of ADHD in the United States or whether the problem is overdiagnosis.

The number of children diagnosed with ADHD has significantly increased, from 7.8 percent in 2003 to 11.0 percent in 2011-2012 for children ages 4 to 17, according to the Centers for Disease Control and Prevention. The number among younger children, ages 2 to 5, jumped by more than 50 percent from 2007 to 2011.

The most recent numbers released by the CDC — which recently changed how it counts ADHD — showed that 9.4 percent of children ages 2 to 17 had been diagnosed, the equivalent of 6.1 million children across the country.

Those numbers have sparked worries of overdiagnosis or misdiagnosis, especially because young children may be prescribed stimulant medications such as Adderall and Ritalin. The long-term effects of those drugs on young brains and bodies have not been well studied, and the side effects include poor appetite, sleeplessness, irritability and slowed growth.

In 2016, the CDC issued a warning, urging parents of preschoolers to try behavior therapy first before putting their children on drugs.

At the same time, as experts’ understanding of ADHD has grown, they warn that there is harm in allowing it to go unaddressed. Untreated ADHD is associated with academic problems in school, higher divorce rates, employment problems and increased risks of physical injury.

Jena said he and a co-author of the study, Timothy Layton, got the idea for their research while discussing Layton’s concerns about whether to “redshirt” his child by holding off an extra year before starting school.

“It got us thinking about the huge difference a year can make at that age of 5, 6, 7,” Jena said.

The researchers used data from a large health insurance database to look at children in states with a strict birthday cutoff policy. Then they studied the ADHD diagnoses for children born in August, who became youngest in their classes, compared with those born in September, who became the oldest in their classes. They found that the August children were 34 percent more likely to be diagnosed with ADHD than the September children.

The study is not the first to identify this phenomenon — other studies in recent years have reported similar findings — but it is among the largest and most rigorous of such studies, said Stephen Hinshaw, a clinical and developmental psychologist at the University of California at Berkeley.

“It’s a well-done study,” said Hinshaw, who has studied ADHD for more than 30 years. “My worry is that many critics will point to this and say: ‘You see, ADHD isn’t a real thing. It’s just immature kids starting school too early.’ Because there’s real danger in that, as well.”

Hinshaw said he believes there are real issues with how ADHD is diagnosed — often after a few minutes in the office of a pediatrician with no specialized training in ADHD. Another reason ADHD may be overdiagnosed, some studies have suggested, is because of increasing pressure on schools to meet test-based performance benchmarks. In some districts, test scores of children with ADHD are excluded from those targets.

“It’s the casual nature of diagnosis that is fueling the problem of overdiagnosis,” Hinshaw said. “But that doesn’t mean ADHD isn’t a problem in our society.”

Undiagnosed ADHD can lead to harming behavior such as self-cutting, experts say, or even suicidal tendencies.

“The longer you go dealing with impairments because of ADHD, the more the effect on your life,” Hinshaw said.

Researchers have documented how the brains of children with ADHD often develop differently, finding that the condition has an inheritable genetic component.

“The problem isn’t overdiagnosis. The problem is when ADHD goes undiagnosed,” said Michael Manos, head of the Cleveland Clinic’s ADHD Center for Evaluation and Treatment. Manos said he has treated adults whose lack of diagnosis has led them to feel like failures. “They hear this message their whole life that something is wrong with them, that they aren’t good enough.”

That is why correctly diagnosing ADHD is so important, said Manos and others.

Jena said the point of his study on school cutoff dates is not to point an accusatory finger at schools and pediatricians for overdiagnosing the problem.

“The big thing here is awareness,” he said. “If you’re a parent concerned your child may have ADHD, you might reasonably ask if your 5-year-old should be put on medication or if he just needs six extra months to mature and catch up with the other kids.”

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