Whether your child is born in January or June could have an impact on whether they're identified as having Attention Deficit Hyperactivity Disorder, or ADHD. That's according to a new study. Now, the British Columbia research is raising concerns about whether some of them are being misdiagnosed.

Even though they're all in the same grade, not every child in a classroom is the same age. Some kids can be as much as a full year younger, if they're born late in the year. And that can make a big difference in how they learn and behave. "What we see is some differences in gross motor skills, can they take on and off clothes well, tie up shoes, work with scissors and things like that," said Howard Ryant, Principal at Collicutt School.

That lack of maturity could have serious consequences. They could end up on medication for ADHD, according to a new study today in the Canadian Medical Association Journal.

The study looked at thousands of children in British Columbia between 6 and 12 years old and found an elevated risk of diagnosis and treatment for ADHD among children born in December compared with January. Children born in December were almost 40 percent more likely to receive the diagnosis than children born in January. December babies were almost 50 percent more likely to receive prescription medication for ADHD. It's a finding that raises concerns about medicating the normal range of childhood behaviors, particularly for boys. "Just labeling a child as having a behavioral disorder that they don't have that could change their self perception, change how they are treated by teachers or by parents, that sort of thing," said Richard Morrow, a health research analyst.

The differences in maturity between kids in the same grade is called the relative age effect. It has been measured in sports skills and in other areas of learning like reading and math.

Jean Shireff, a 2nd grade teacher, says the differences in behavior even out over time. "I would say, people might panic and think, "Oh my God, they're ADHD", where more they are just immature at that point in their lives, and they haven't grown into who they are going to be in that grade or in that year," Shireff said.

In other words, a behavioral problem might simply be because the child is just a little bit younger than the rest of the class.

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Information courtesy of NBC News.