ADHD diagnosis more likely for kids born later in the year: study Add to ... Researchers in British Columbia have discovered that children born in the latter months of the year are more likely to be diagnosed with attention deficit hyperactivity disorder than their peers born earlier in the year. The study, published Monday in the Canadian Medical Association Journal, found those children are also more likely to be placed on medication, some of which may be linked to side effects. video The finding should serve as a wake-up call for educators, parents and the public about the hazards of properly diagnosing ADHD. It raises serious questions about whether certain behaviours, such as restlessness or inability to concentrate, are leaving younger, more immature classmates vulnerable to an inaccurate diagnosis of ADHD than their older, more developed peers. "What's clear is that relative age is influencing who receives this diagnosis and who receives treatment for ADHD," said Richard Morrow, lead author of the study and health research analyst of the Therapeutics Initiative at the University of British Columbia. "It seems to be that sometimes a child's ... lack of maturity can sometimes be mistaken for ... a diagnosis. The scale of the study also sets it apart -- it is the largest of its kind. After looking at more than 937,000 children between ages 6 and 12 from 1997 to 2008, the researchers found those born in December were 39 per cent more likely to be diagnosed with ADHD and 48