An 11-year Canadian study suggests the youngest children in a classroom are more likely to be assessed as having attention deficit hyperactivity disorder (ADHD) compared to their older classmates, raising concerns that many schoolchildren are wrongly being diagnosed and prescribed medication.  

University of British Columbia researchers focused on 937,943 students who were six to 12 years old between Dec. 1, 1997, and Nov. 30, 2008 in a province where the cutoff age for entry to school is Dec. 31. The study, published in Monday's Canadian Medical Association Journal, found children born in December were 39 per cent more likely to be diagnosed and 48 per cent more likely to be treated with medication for ADHD, compared to children with a January birthday.

Some facts about ADHD:

  • A developmental disorder usually diagnosed in childhood or adolescence. Symptoms include hyperactivity, impulsivity, distractibility.
  • Affects five to 15 per cent of school-aged children, occurring more frequently in boys than girls.
  • Research suggests it's caused by neurological imbalances in the brain.
  • Treatment may include methylphenidate (Ritalin), lisdexamfetamine (Vyvanse) or dextroamphetamine (Dexedrine) to stimulate brain chemicals, Atomoxetine (Strattera) to help with concentration, counselling, parent training in child behaviour management and classroom behaviour modification.

"The relative maturity of children is affecting the diagnosis, so in other words, the lack of maturity in younger children is making them more likely to get the diagnosis, and we can interpret that as the fact that sometimes a lack of maturity is being misinterpreted as symptoms of a neurobehavioural disorder of ADHD," the study's lead author, Richard Morrow, health research analyst with the Therapeutics Initiative at the University of British Columbia, told CBC News.

As a result, he says, there are concerns that ADHD — the most commonly diagnosed neurobehavioural disorder in children — is being overdiagnosed and overtreated in younger students in a classroom.

Exposing kids to unnecessary drugs a concern

In a news release, Morrow said: "Our study suggests younger, less mature children are inappropriately being labelled and treated. It is important not to expose children to potential harms from unnecessary diagnosis and use of medications."

The cutoff age for children entering school for the first time (either kindergarten or Grade 1) in B.C. and other provinces is Dec. 31. That means some students with December birthdays could be nearly a full year younger than other kids in their class. Those younger students may also appear to be immature, something researchers have labelled as the "relative-age effect," which could also influence both academic and athletic performance.

The UBC study notes that two recent studies using survey and private health plan data in the U.S. concluded that date of birth and the age at which patients started school were predictors of diagnosis and treatment of ADHD. The B.C. researchers looked to determine whether the relative-age effect was also present in Canada.

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The researchers also stressed there are significant health and social ramifications of a wrong diagnosis of ADHD. Medications (which are largely stimulants, but a non-stimulant can also be used) can have negative health effects in children that can include sleep disruption, increased risk of cardiovascular events and slower growth rates, they said

The ADHD medications included in the study were

  • Methylphenidate.
  • Dextroamphetamine (a stimulant).
  • Mixed amphetamine salts.
  • Atomoxetine.

Behaviour at home should be considered

As well, researchers added, younger children who have been labelled as having ADHD may be treated differently by teachers and parents, which could lead to negative self-perception and social issues. 

The study recommends that when assessing whether a child has ADHD, the student's age compared to his or her classmates, as well as behaviour outside school should be taken into account.

Howard Ryant, principal at Collicutt elementary school in Winnipeg, says it's not commonplace for educators to look to a child's birth month if behavioural or developmental issues come up.

"Sometimes ... when a child is having problems, we look at the month that they were born in and we say, 'Well, yeah, maybe that's because the kid's a December kid,' but it's usually after the fact. We don't go into it looking that the kid is going to be less mature because [he or she is] born later in the year."

Funding for the UBC study was provided by the Canadian Institutes of Health research and the B.C. Ministry of Health.