Is Starting School Early Linked to ADHD?

Is it possible that the month and year in which a child is born is an indicator of the likelihood they’ll be diagnosed with Attention Deficit Hyperactivity Disorder (ADHD?)

Is early age admission to school a factor in the likelihood of diagnosis with ADHD?

Is it possible that some, perhaps many, ADHD diagnoses are the result of a child being held to a new and higher behavioral standard for which they are not developmentally ready?

While the answer to all of these questions appears to be “yes,” the last one may cancel out the first two.

In a 2018 research study, scientists at Harvard Medical School found that children born in August in states with a September 1 enrollment cutoff date were at a significantly higher likelihood of being misdiagnosed with ADHD than other children. Their findings were published November 28, 2018 in The New England Journal of Medicine, and the researchers showed that August-born children in September 1 cutoff states are 30% more likely to receive a positive ADHD diagnosis than other, slightly older children enrolled in the same grade.(1)

The start of kindergarten can be a huge deal for kids and their families. It’s a milestone, full of photo opportunities, tears from mom and dad (and sometimes the kids) and new friends and experiences. But parents of late summer babies are also faced with a difficult decision. Do they allow their little baby to be among the youngest in class or hold him or her back until next year?

The latter choice may be the wise one, if the Harvard research is right. Giving these July and August babies one more year to develop more intellectual maturity, emotional maturity, cognition and attention skills may not only improve their academic chances, but avoid being misdiagnosed with a behavioral neurological disorder.

The rate at which kids are being diagnosed with ADHD has exploded in recent years. According to CDC data, in 2016 5.2% of all American children aged 2-17 were being medicated for ADHD. (2) What’s driving this increase?

Certainly, we’ve gotten better at recognizing and identifying ADHD and other neurological and behavioral disorders. There is likely also an actual rise in the prevalence of ADHD. However, some doctors, researchers and even some parents are beginning to suspect an additional cause: misdiagnosis.

The results of the Harvard study certainly seem to reinforce the latter cause. For at least one subset of elementary school kids, the diagnosis of ADHD may be related more to early school enrollment than any real, underlying problem, according to the researchers.

“Our findings suggest the possibility that large numbers of kids are being over-diagnosed and overtreated for ADHD because they happen to be relatively immature compared to their older classmates in the early years of elementary school,” said study lead author Timothy Layton, assistant professor of health care policy in the Blavatnik Institute at Harvard Medical School.

Think about this. The majority of US states have arbitrary cutoff dates for deciding when a child can start kindergarten and school and in which grade they will be placed. If your state has a September 1 cutoff and your child was born on August 31, your child is nearly a full year younger than the oldest possible child in his or her class, who was born September 1.


For kindergarten, this might mean a child starting school shortly after their birthday on August 31 may be as young as 5. Other children may be a year or more older than that child, if the child was “red-shirted,” or held out of school for an additional year before kindergarten. The term is borrowed from the scholastic sports world, where it means to keep a player out of full competition to allow them to train and develop for an extra year.

A year can make a huge difference when we’re talking about 5, 6 and 7 year-olds. Layton noted that, at this age, the younger student may have difficulty with attention, a harder time sitting still for long periods of time and may lack concentration skills. Fidgeting and apparent inattentiveness may lead to a medical referral, followed by (mis)diagnosis and treatment for ADHD.

So what is perfectly normal behavior for an active 6 year-old will be held against a “higher” standard set by the older students in the same class. Of course, under this lens, the behavior would seem abnormal relative to the other, older students.

The 11- or 12-month difference will create an extreme dynamic in behavior differences among younger children, according to researchers.

“As children grow older, small differences in age equalize and dissipate over time, but behaviorally speaking, the difference between a 6-year-old and a 7-year-old could be quite pronounced,” said study senior author Anupam Jena, the Ruth L. Newhouse Associate Professor of Health Care Policy in the Blavatnik Institute at Harvard Medical School and an internal medicine physician at Massachusetts General Hospital. “A normal behavior may appear anomalous relative to the child’s peer group.”

The team dug into the records of a large insurance database to examine and compare the difference in ADHD diagnosis between August and September birth months. Their sample included over 407,000 elementary school children born between 2007 and 2009. They followed the children through the end of 2015.

Their work revealed a 30% greater likelihood of an ADHD diagnosis for children born in August in states with a September 1 school enrollment cutoff than for those children born in September. They found no such correlation between August- and September-born children in states with cutoff dates other than September 1 for enrollment in school.

The evidence is in the numbers. For students born in August in states with September 1 enrollment cut-off dates, 85 out of 100,000 were diagnosed with or treated for ADHD. That compares to only 64 of 100,000 September-born children. The differential was also significant when researchers considered only those children treated for ADHD. 53 out of 100,000 students born in August were treated for ADHD versus 40 out of 100,000 of those born in September.

When you factor everything in, the question naturally arises about whether all the diagnoses are accurate and legitimate. Do all these children really have ADHD? Or are we missing something? Are teachers and doctors seeing normal 5 year-old behavior and categorizing it as a disorder? As a result, are we medicating a significant percentage of our kids for no reason?

The answer is a resounding “maybe.” Sure, some of the kids in question do have ADHD and will benefit from therapies. Many do not. They simply need more time to develop and mature before being expected to live up to a more mature standard.

ADHD or age-appropriate behavior?

All of this seems like an argument in favor of red-shirting summer babies who are at the youngest end of the kindergarten spectrum. The arguments in favor of red-shirting rely on the reality that kindergarten has shifted focus from socialization and play to a more academic orientation. The arguments against it include the consistently rising cost of preschool and daycare. Many families simply can’t afford an extra year of either or both.

For parents who can’t red-shirt, Layton advises parents that they “should also do everything they can to help their children weather the storm of being the youngest child in their class, which brings with it numerous disadvantages for the child.”

Layton suggested that, if at all possible, parents of summer babies consider holding them back a year. This would allow them to be the oldest in class instead of the youngest.

He also told Healthline “I think parents of children with summer birthdays (or birthdays close to the cutoff in their state) should be skeptical when teachers come to them suggesting their child has ADHD.”

Does any of this really have long-term implications? Yes, says Jena. He correlates it to a phenomenon that Malcolm Gladwell discussed in his book Outliers. Research has shown that Canadian children born early in the year who play hockey have a statistically better chance of reaching the professional levels than their later-born peers. Youth hockey leagues in Canada use a January 1 cutoff date for their age groups. As a result, younger players born early in the year are older and more mature. This seems to increase the likelihood that they will be tracked into elite leagues, receive better coaching with more ice time and more talented teammates and competition. This creates a cumulative advantage over time, giving the relatively older players a skill and development edge over the younger players.

A similar outcome was noted in a 2017 working paper from the National Bureau of Economic Research with relation to education. Their research suggested that children born just after the cutoff date have better long-term educational performance and outcomes than their relatively younger age-group peers

“In all of those scenarios, timing and age appear to be potent influencers of outcome,” Jena said.

While the Harvard team concerned themselves with the potential for over-diagnosis or misdiagnosis, other medical professionals and researchers are worried about under-diagnosis. Dr. Mark Wolraich, professor of pediatrics at Oklahoma State University and Chief of the Section of Development and Behavioral Pediatrics there, told Healthline that while over-diagnosis may be a real issue, he fears there may be a considerable amount of under-diagnosis of ADHD.

He’s worried that fear over over-diagnosis or misdiagnosis may prevent those kids who truly need help from getting the right diagnosis.

“One of the important aspects of making the diagnosis is determining if the symptoms are impairing the child’s function,” he said. “Those children who are having problems need to have those problems addressed, because the experience with failure and not doing well can be very negative for these kids.”

Wolraich also believes it’s crucial for doctors and others in the diagnostic process to consider the child’s environment, including their school and teachers. He also stresses that ADHD isn’t necessarily a permanent diagnosis. “Clearly, if they improve with maturity, they no longer have a diagnosis,” he said. (3)

There are significant regional variations in both diagnosis and treatment for ADHD in the United States. Diagnosis and treatment rates are climbing across the US. More financial resources are being committed to managing ADHD and other neuro-behavioral disorders at the school system level. All of these factors raise sensitivity levels regarding ADHD over-diagnosis and over-treatment.

According to Jena, there are complex and multi-factoral influences on the prevalence of ADHD and the rise in case numbers. He believes arbitrary cutoff dates or school enrollment are one of the variables involved. Many states are now holding schools accountable for identifying ADHD and giving educators incentives for referring children for medical evaluation who exhibit any symptoms that suggest ADHD.


“The diagnosis of this condition is not just related to the symptoms, it’s related to the context,” Jena said. “The relative age of the kids in class, laws and regulations, and other circumstances all come together.”

Jena believes all factors influencing the diagnosis (or not) of ADHD should be considered before prescribing treatment. “A child’s age relative to his or her peers in the same grade should be taken into consideration and the reasons for referral carefully examined,” he said.

So what now? Here, I believe, are the two big things to take away from this study and the context surrounding it.

First, doctors and teachers need to give better consideration to a not just a child’s age, but their maturity level when assessing behavior. Being boisterous, fidgety or just different from their class-level peers isn’t necessarily grounds for a psychiatric diagnosis. It surely shouldn’t be the only reason to medicate a child. The majority of the kids in question most likely need a little time to mature and adjust to new surroundings, rules and expectations, not psychoactive medication.

Second, all of us should get better at dealing with the relative age and maturity level differences that exist among any group of kids and in just about every classroom. Let’s be patient and supportive while these kids are growing into what we expect them to do, be and master. Each of them is in a slightly different place, seeing a new world from their own perspective. Let’s see that and help them grow into what they are capable of, without medication, labels or stigma. Let’s support educators, too. Many of them understand what needs to be done, but too often administrators have unreasonable expectations of “the classroom.” Parents, too, need to take a step back when behavioral “issues” arise and ask if this is related to maturity levels or a real behavioral condition.

Last, maybe it’s time to stop asking 5 and 6 year-olds to act like adults. They’re exploring the world with minds full of wonder. Perhaps if we stifled that less and gave them more age-appropriate activities and learning opportunities, we’d see a different side of them. Asking 5 year-olds to do what 6, 7 and even 8 or 9 year-olds can do isn’t a problem with the 5 year-old, it’s a problem with adults.

Keep the faith and keep after it!

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  1. Timothy J. Layton, Michael L. Barnett, Tanner R. Hicks, Anupam B. Jena. Attention Deficit–Hyperactivity Disorder and Month of School Enrollment. New England Journal of Medicine, 2018

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