In North America, children begin their formal academic education in kindergarten. Different regions throughout the United States and Canada have different entry dates for school admittance. The birth month of a child determines what year they will enter school. Children whose birthdays fall closest to the cutoff date are the youngest members of their grade, while those whose birthdays fall immediately after the cutoff date are the oldest. This results in classrooms teaching to children that can be a full year apart in age. Although this does not usually present an issue for most children, some children who develop behavioral maturity later than others may have difficulty keeping up with their classmates. The birth season of a child can significantly impact how their social, academic, and behavioral skills are in relation to their peers. This is one reason that experts believe the rates of attention-deficit hyperactivity disorder (ADHD) diagnoses are disproportionately high among the youngest students in American classrooms.
The topic of birth season has been explored with relation to other mental issues, including autism and schizophrenia. However, little research has focused on how relative age influences ADHD diagnoses in various countries. To determine if the social and medical differences between Canada and America would impact the rates of diagnoses in each country, Richard L. Morrow of the Department of Anesthesiology, Pharmacology and Therapeutics at the University of British Columbia led an 11-year study that looked at the rates of ADHD among nearly one million children ranging in age from 6 to 12 years. He categorized them based on birth season and reviewed which children were prescribed medication for ADHD.
In Canada, the cutoff date for birthdate to enter school is December 31. When he analyzed the results, Morrow found that the boys with December birthdays had more than a 30% higher risk for ADHD diagnosis than those who were born only 1 month later. For girls, the likelihood of being diagnosed was 70% higher if they were born in December. Morrow also discovered that the children with December birthdays were more likely to be on medication than those with January birthdates. These findings support the relative-age theory and suggest that the youngest children in a class may be at a much higher risk for overdiagnosis of ADHD than those who, by entry date guidelines, are only days younger but are a full grade behind. This underscores the importance of considering age and maturity when evaluating teacher and parent ratings of children. Morrow added, “It is possible that closer consideration of a child’s behavior in multiple contexts, including those outside of school, may lessen the risk of unnecessary diagnosis when assessing children for ADHD.”
Morrow, R. L., Garland, E. J., Wright, J. M., Maclure, M., Taylor, S. (2012). Influence of relative age on diagnosis and treatment of attention-deficit/hyperactivity disorder in children: CMAJ. Canadian Medical Association Journal, 184.7, 755.
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