Youngest Children In A Class Are Most Likely To Get ADHD Diagnosis

Nov 28, 2018
Originally published on November 30, 2018 4:25 pm

The youngest children in a school class are most likely to be diagnosed with attention deficit hyperactivity disorder, when in fact their comparatively fidgety behavior may be due to their relative immaturity, according to a study published online Wednesday.

Scientists from Harvard University probed the way ADHD is assessed by taking advantage of a quirk found in many U.S. school systems: There's a Sept. 1 cutoff for enrolling in kindergarten. That means children born in August get in just under the wire, while children with September birthdays have had to wait until the following school year to enroll.

"You could certainly imagine a scenario in which two kids who are in a class who are different in age by almost a year could be viewed very differently by a teacher, or school personnel who's evaluating them," says Dr. Anupam Jena, a physician and economist at Harvard Medical School. "A year of age difference in a 5-year-old or a 6-year-old is huge."

Scouring a database of insurance claims encompassing more than 400,000 children, the researchers categorized children by their month of birth. And the report in the New England Journal of Medicine finds that the youngest children in the classroom — those born in August — were about 35 percent more likely to get a diagnosis of ADHD and to be treated for the condition.

ADHD was diagnosed in 0.8 percent of children born in August versus 0.6 percent of the older, September-born children. Nationally, ADHD diagnosis rates are about 5 percent, but that includes children 2 to 17, while this study focused on children ages 4 to 7.

The scientists didn't find this difference in states that don't enforce a Sept. 1 enrollment date, and they didn't find any other health differences among the August-born children in the study.

This result matters for the individual children who may have been inappropriately diagnosed and treated. "You want to be careful about starting a young child on this medication,"Jena says.

But the enrollment effect only explains a small proportion of ADHD. For the youngest – August-born children — Jena says perhaps 1 in 4 of their diagnoses could be inappropriate.

"Teachers, counselors, principals – those individuals should be aware of this possibility," Jena says. School personnel are the most likely to raise an ADHD flag and suggest that parents get their children seen by a pediatrician.

Jeffrey Newcorn, a psychiatrist and pediatrician who heads the division of ADHD and learning disorders at Mount Sinai Medical Center in New York, says the study adds to the scientific discussion around ADHD. But, he says, "I would be very careful about reading this as if the kids are misdiagnosed."

You may be more likely to identify ADHD in the youngest children in their grade, he says, but maybe that's no more than an early diagnosis, which would have happened in a year or two anyway.

Several other studies have suggested that ADHD is more likely to be diagnosed among children who are among the youngest in their classes.

"The current study is convincing because of its large sample size and the use of actual insurance records of diagnosis, rather than more subjective recall," psychology professor Stephen Hinshaw, a longtime ADHD researcher at the University of California, Berkeley, writes in an email.

These results underscore the shortcomings in how ADHD is identified, Hinshaw writes in an email. "Indeed, many issues in childhood can 'look' like ADHD: trauma, overcrowded classrooms, medical conditions (e.g., seizures), or other psychiatric issues (e.g., anxiety, depression). So, a cursory, brief office visit is not up to the task!"

Results that rely on health insurance data lack important details.

"We really don't know much about the 'why' and the 'how' of these results," says Meredith Bergey, a sociologist at Villanova University. It's hard to tease out how these diagnoses were arrived at, based simply on data from the insurance records.

ADHD isn't a simple diagnosis like an ear infection. So Bergey argues that it should be a more deliberative process. "What if the teacher were actually there along with the parent and the physicians?" she asks. That would better inform a diagnosis, and factor in potentially important factors such as the age of the child.

You can contact NPR Science Correspondent Richard Harris at

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Sometimes children might get diagnosed with attention deficit and hyperactivity disorder simply because they are younger than their peers and not because of a medical condition. That's one way to interpret a study published online today in The New England Journal of Medicine. NPR's Richard Harris reports.

RICHARD HARRIS, BYLINE: Attention deficit hyperactivity disorder is on the rise in the United States and is being diagnosed even in preschool children. Anupam Jena and his colleagues at Harvard Medical School decided to follow up on studies suggesting that the youngest children in a class were more likely to get an ADHD diagnosis than their relatively mature classmates.

ANUPAM JENA: ADHD is a condition which a lot of people think might be overdiagnosed, and you could certainly imagine a scenario in which two kids who were in a class who are different in age by almost a year could be viewed very differently by a teacher or school personnel who's evaluating them.

HARRIS: The researchers relied on a quirk of school enrollment in order to identify the youngest and oldest children in a class. Many states have a cutoff that says children born after September 1 have to wait a year to enroll in kindergarten. The children with August birth dates come in just under the wire, so they're almost a year younger than the oldest kids in the class.

JENA: A year of age difference in the 5-year-old, 6-year-old is huge.

HARRIS: Jena and his colleagues had a huge database of health insurance claims. They sorted kids by their birth month, then asked a simple question - whether the youngest kids were more likely to be diagnosed and treated for ADHD when compared with the oldest kids in the class. Looking at children ages 4 through 7, they conclude the answer was yes.

JENA: The kids who were born in August have about a 35 percent higher rate of diagnosis and medical treatment compared to the children who were born in September.

HARRIS: This makes a big difference to the individual children diagnosed with ADHD, but it has only a small effect on the overall number of ADHD diagnoses nationwide, Jena says. It's even a relatively small effect for the youngest children in a class, those born in August.

JENA: It could be the case that as much as a quarter of the diagnoses that are occurring in August may be inappropriate.

HARRIS: Jeffrey Newcorn, a psychiatrist and pediatrician who runs the ADHD division at Mount Sinai in New York, finds the results intriguing, but he interprets the study cautiously.

JEFFREY NEWCORN: I don't think it says anything about overdiagnosis.

HARRIS: In his view, this says a lot more about identifying kids with ADHD.

NEWCORN: Maybe you're going to be more inclined to call that younger kid ADHD when you wouldn't if you put them in a younger grade, but maybe in a year or two, you would anyway.

HARRIS: Newcorn says, in any event, he considers whether a child is among the youngest or the oldest in class when evaluating someone for ADHD. This whole conversation highlights the challenge of making a diagnosis, which is based on a lot of input from teachers and parents, not any kind of medical test. Meredith Bergey, a sociologist at Villanova University, says the new study underscores the need for a careful evaluation of signs and symptoms in the doctor's office.

MEREDITH BERGEY: What if the teacher were actually there in that conversation with the physicians, with the parents? And there needs to be a lot more, I would argue, conversation across stakeholders who are involved in making an ADHD diagnosis and dealing with ADHD treatment.

HARRIS: ADHD is increasingly diagnosed in very young children and is diagnosed far more often in the United States than elsewhere. So social context matters a lot. And that's why she finds the study that highlights differences of diagnosis based on relative age intriguing. Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.