Youngest Kids in Class May Be at Higher Risk for ADHD

Published March 21, 2016

As ADHD diagnoses continue to rise, parents wonder what environmental or genetic factors — like lead exposure, low birth weight, or genetic mutations — may be putting their child at risk. Now, a new concern might be added to that list: Children who are the youngest in their class might be more at risk for getting diagnosed with ADHD.

A new study from Taiwan, published recently in the Journal of Pediatrics, examined data from more than 300,000 children born between 1997 and 2011. Like many school districts in the United States, Taiwan has an August 31 cutoff date; children born in August are the youngest in their grade, while children born in September are the oldest. The study found that both boys and girls born in August were 75 percent more likely to be diagnosed with ADHD than those with September birthdays. The boys with August birthdays were doubly affected: They were found to be 74 percent more likely to receive medication than their September counterparts, even if both boys had been diagnosed with ADHD.

Past studies from around the world — including Canada, Israel, and Sweden — have all shown similar results. A study in Iceland found that the youngest children in each grade were between 20 and 100 percent more likely to be diagnosed with ADHD. The only country where the pattern didn’t hold true was Denmark, where parents have more flexibility in deciding when their child will enter school.

In the U.S. and around the world, kids generally begin first grade at age six. At that age, a few months can mean the difference between “developmentally appropriate” and “behind,” and children with birthdays close to the cutoff may be almost a full year younger than the oldest children in their class. Since ADHD is generally diagnosed using input from parents and teachers, it often means that children are directly measured against the most mature students in their grade — making them seem overactive or less focused by comparison.

A common solution to this problem — apart from ADHD diagnosis and treatment — is to have a child repeat a grade to “catch up,” but more and more educators are recognizing the flaws in this approach.

"There is absolutely no data to support grade repetition for maturity issues,” says Dr. Adiaha Spinks-Franklin, a Texas-based pediatrician who was not involved in the Taiwanese study. “Children who repeat a grade are at a higher risk of dropping out of high school. They are more likely to be bullied."

So what else can parents, teachers, and doctors do? Researchers suggest that parents of August babies try waiting a few years to see if the child “grows out of” her symptoms as she matures. By the time children reach their early teens, most of the developmental gaps between the oldest and youngest in a particular grade disappear.

To Helga Zoëga, a researcher who worked on the Icelandic and Israeli studies, the solution is even more straightforward: “Just treat the individual according to his or her age."

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