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Youngest Kids in a Grade More Likely to Have ADHD Diagnosis, New Study Shows

By Alexis Clark, MA, MS on

A new study shows that the youngest kids in a school grade are more likely to be diagnosed with ADHD than the oldest kids in the same grade.

The study was published in The New England Journal of Medicine. Using a large insurance database, researchers looked at 407,846 kids born across the United States from 2007 to 2009. They followed these kids until 2015, when they entered grade school.

Past studies have had similar results. But this is one of the largest studies to date on the impact of age within a grade on ADHD diagnosis.

We asked Understood experts Thomas E. Brown, Mark Griffin and Preetika Mukherjee to weigh in on the study.

Key Findings

The study focused on states that require kids to turn 5 years old by September 1 to enroll in kindergarten. This means kids born in August can start school, and kids born after September 1 must wait a year. As a result, August-born kids are the youngest in their grade, and September-born kids the oldest.

The researchers found that August-born kids had a 32 percent higher rate of ADHD diagnosis than September-born kids. They also had a 34 percent higher rate of treatment with ADHD medication.

These numbers were different for boys and girls. Being youngest in a grade seemed to be more significant for boys. Boys who were the youngest in their class were 37 percent more likely to be diagnosed with ADHD, while girls were only 28 percent more likely.

Researchers also looked at states without a September 1 age cutoff. In those states, there was no difference in ADHD diagnosis or treatment rates between kids born in August or September.

Key Takeaways for Parents

Griffin says the study was generally reliable. “There’s a 12-month span of ages within a grade,” he says, “so the youngest kids may have more inattentive behavior. And it’s possible that behavior could be compared to older kids and lead to an ADHD diagnosis.”

But there are some big limitations to the study. Brown notes that they couldn’t assess if any of the kids had been misdiagnosed with ADHD. “They can only say that relative age in a grade impacts ADHD diagnosis,” he says. “And they can’t say that the impact is helpful or harmful.”

For instance, the study notes that the youngest kids in a grade tend to have worse academics in school. So those kids may benefit from the extra support that can come with an ADHD diagnosis.

All of the experts agreed it’s important to get a good evaluation if you’re concerned your child has ADHD. “There are objective criteria to diagnose ADHD. A child has to meet six (or more) symptoms to meet the diagnostic criteria,” says Mukherjee.

“A specialist who evaluates your child should consider all explanations for inattentive or impulsive behavior,” she explains. “There could be personal circumstances, like being younger in a grade. Or there could be other co-occurring issues.”

Griffin recommends being active in the process. “Keep a log of your child’s behavior in kindergarten. Make sure your voice is heard during any assessment of your child’s behavior,” he advises. “Find out what the expectations are for kids in kindergarten and how your child matches up developmentally.”

Redshirting, or waiting a year to enroll in school is also an option,” says Brown. “If your child is on the younger end of his age group and seems immature for his age, it might be preferable to have one more year of preschool.”


Learn more about ADHD symptoms at different ages. Find out how early ADHD can be diagnosed. And watch a video of an expert explaining how ADHD symptoms can change over time.

Any opinions, views, information and other content contained in blogs on Understood.org are the sole responsibility of the writer of the blog, and do not necessarily reflect the views, values, opinions or beliefs of, and are not endorsed by, Understood.

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