New Research Shows Link Between Kindergarten Cutoff Dates And ADHD Diagnosis

A new study released Wednesday shows kids who just made the cutoff date for kindergarten entry are more likely to be diagnosed with attention deficit-hyperactivity disorder, commonly known as ADHD.

Harvard Medical School researchers examined data from 18 states which required children turn 5 years old by September 1 in order to enroll in kindergarten. Kids born in August could be 11 to 12 months younger than their classmates who were born in September.

The results, published in the New England Journal of Medicine, showed that students born in August had a 34 percent higher rate of ADHD diagnosis than their older classmates born in September.

Essentially, that means the youngest children in school are more likely to be diagnosed with ADHD.

Furthermore, younger students are more prone to receiving longer, more intensive medical treatments for ADHD than older classmates. That especially surprised the study's main author, Timothy Layton, an assistant professor of Health Care Policy at Harvard Medical School.

“Our assumption was that, for those cases, there would be fewer prescriptions and less intensive treatment,” Layton said. “We found the opposite. They’re not getting mild diagnosis and treatment for ADHD. They’re being treated intensively, which is more concerning.”

According to a 2016 CDC report, nearly one in 10 children between 2 and 17 years of age — over 6.1 million total — have been diagnosed with ADHD across the nation. And the rates of ADHD diagnosis have increased by more than 40 percent over the past two decades.

But Layton believes normal maturity differences between younger students versus their older classmates are being overlooked as a factor in ADHD diagnoses, especially among young students.

"The difference in normal behavior between a 5-year-old and a 6-year-old is actually quite large," Layton explained. "But that's probably not something [teachers] are really thinking about. They just observe that they have a class of children who are about the same age, and they may attribute frequent misbehavior to ADHD rather than to normal variation in child behavior based on age."

Layton says his interest in this data came largely out of concern for his own son, Soren.

“[Soren]’s fifth birthday was close to the cutoff last year,” Layton said, “and we made the decision to hold him back. We saw research showing that kids born before the August cutoff and were young for their class really had an uphill battle.”

"The difference in normal behavior between a 5-year-old and a 6-year-old is actually quite large."

Timothy Layton, Harvard Medical School

Massachusetts allows school districts to determine their own cutoff dates. The vast majority have cutoff dates between Aug. 1 and Sept. 8.

Though his son has not been diagnosed with ADHD, Layton worries both that young children are being misdiagnosed, and also that the long-term consequences of such intensive treatments for ADHD aren’t fully understood.

Those concerns may resonate with Meaghan O’Neill, who has firsthand experience living with a child struggling with ADHD. Her 12-year-old son Nick was diagnosed when he was in the third grade.

She said she hopes this study prompts some re-evaluation of how children are diagnosed with ADHD and how their behavior is viewed by teachers and parents alike.

“I personally think that kindergarten is too young to diagnose [ADHD],” says O’Neill. “There are symptoms that seem like it could be ADHD, but you really don't know because part of it is just kids being kids, being a little bit energetic and not knowing how to sit still.”

Layton agreed.

“Our work definitely shows that the diagnosis of ADHD is far from an exact science,” he says. “We have more objective ways to diagnose this condition especially because this condition is so often tied to drug treatment.”

Layton also expected there could be a shift in how parents would choose to enroll their children in schools as a result of these new concerns. He thinks more parents will start opting to hold their children back a year if they’re close to a cutoff date, as he did with his son.

“It’s already happening. In fact, after we held our son back, we found out that if he would have started at the normal time, the next youngest kid in his class had a May birthday. And so it seems like there's kind of an arms race among parents to not have their kid be the youngest [in their class].”

But whether or not parents hold their children back more frequently, Layton hoped this data will encourage doctors, parents and teachers to view child behaviors with more context.

"My hope is that when parents come in and say 'my kid's teacher says he has symptoms condition consistent with ADHD,' that the physician pauses," Layton said. "And if that child had a summer birthday, they say, 'Wait a minute. Let's consider the child's age relative to their their cohort.'"

Correction: A previous version of this article stated that children born in August could be 11 to 12 months older than their September-born classmates. It should have said "younger." We regret the error.