Youngest kids in class more likely to be diagnosed with ADHD

Psychiatrists estimate that about 3% to 7% of school children have ADHD.

Story highlights

  • Younger children more likely to be diagnosed for what may simply be immaturity
  • Problems with attentiveness and hyperactivity fall along a continuum
  • A child should have at least two doctor's visits along with his or her parents
Children who are the youngest in their class are more likely than their older classmates to be diagnosed and given medication for attention-deficit hyperactivity disorder (ADHD) -- suggesting that immaturity may be part of the problem, not ADHD.
The finding is from a study of more than 900,000 Canadian children aged 6 to 12, and it dovetails with two U.S. studies that found the same thing in 2010.
In fact, the youngest boys were 30% more likely than their oldest classmates to get an ADHD diagnosis, and the youngest girls had a 70% greater chance, according to the study conducted by Dr. E. Jane Garland, a child and adolescent psychiatrist at the University of British Columbia in Vancouver and colleagues.
"The younger children in a grade were significantly more likely to be diagnosed, labeled, and treated with medication for what in some of them must simply be immaturity," Garland says.
The researchers looked at children born in December, the month before the cutoff date for starting school (in this case, December 31), who were therefore the youngest in their class. They compared those children to youngsters born in January, who missed the cutoff date and so were the oldest in their class -- almost a full year older than those with December birthdays.
Of the boys born in December, 7.4% were diagnosed with ADHD and 6.2% were given medication. In contrast, only 5.7% of boys born in January were diagnosed with ADHD and 4.4% were given ADHD medication. Similarly, 2.7% of girls with December birthdays were diagnosed with ADHD and 1.9% were given ADHD medication, while 1.6% of girls born in January were diagnosed with ADHD and 1.1% were given medication.
As for children born in other months, the younger they were relative to their classmates, the more likely they were to be diagnosed with and treated for ADHD.
The study, published in the Canadian Medical Association Journal, included 937,943 children who were 6 to 12 years old between December 1997 and November 30, 2008, representing all children in this age group in the province of British Columbia.
"It definitely looks like it's a real effect, we now have three studies, and it would be good to know more about it," says Joel Nigg, PhD, a professor of psychiatry and behavioral neuroscience at Oregon Health & Science University in Portland. Nigg studies ADHD, but did not take part in Garland's research.
Diagnosing ADHD can be tricky. For one thing, problems with attentiveness and hyperactivity fall along a continuum, says Garland.
"The symptoms of ADHD are very nonspecific," she says. "If someone is tired or they haven't eaten breakfast, they'll be fidgety and unfocused." There's no lab test that says yes, you have ADHD, or no, you don't, she notes.
Dr. James Perrin, the director of the division of general pediatrics at the Mass General Hospital for Children in Boston, says it takes more than