Findings from a study published in the Journal of Child Psychology and Psychiatry suggest that children who are the youngest in their classroom are more likely to be diagnosed with attention deficit hyperactivity disorder (ADHD) than their older classmates.

Martin Whitely and colleagues conducted a systematic review of 22 studies that examined the relationship between a child’s age relative to their classmates and their chances of being diagnosed with, or medicated for, ADHD. The findings showed that:

• Seventeen studies (with a total of more than 14 million children) found that it was more common for the youngest children in a school year to be diagnosed as ADHD than their older classmates.
• This effect was found for both countries that have a high diagnosis rate, like the USA, Canada and Iceland, and countries where diagnosis is less common, like Finland and Sweden.

The researchers suggest that some teachers may be mistaking normal age-related immaturity of the youngest children in their class for ADHD, and that these findings highlight the importance of being aware of the impact of relative age and give the youngest children in class the extra time they may need to mature.

Source: Whitely, M., Raven, M., Timimi, S., Jureidini, J., Phillimore, J., Leo, J., … & Landman, P. (2018). Attention deficit hyperactivity disorder late birthdate effect common in both high and low prescribing international jurisdictions: systematic review. Journal of Child Psychology and Psychiatry, Advance online publication. doi :10.1111/jcpp.12991