Linking school-age entry and ADHD

Researchers found that children were 39% more likely to be diagnosed, and 48% more likely to be treated with medication for ADHD, if born in December, compared to January. 

Due to the 31 December cut-off birth date for entry into school in British Columbia, children born in December would typically be almost a year younger than their classmates born in January.

Younger children in the same grade as children who may be almost a year older may appear to be immature compared with their older peers. 

This apparent lag in maturity has been called the “relative-age effect”, and influences both academic and athletic performance, the authors said.

http://www.cmaj.ca/content/early/2012/03/05/cmaj.111619