ADHD News & Research

Youngest Students In Each Grade More Likely to Be Diagnosed with ADHD

A large, population-based study of Finnish children further confirms the theory that the youngest children in any classroom are more likely to be singled out as having ADHD.




November 30, 2017

A new study from Finland confirms the findings of earlier studies from Taiwan, Canada, Israel, and other nations: The youngest students in any academic grade are more likely to be diagnosed with ADHD. And conversely, children who are older than their same-grade peers are at greater risk of having their ADHD symptoms overlooked.

“Relative age” refers to a child’s age in relation to other children in the same grade. In Finland, children born in January of each year are the oldest in their grade; children born in December are the youngest. Using a national registry of all children born in Finland between 1991 and 2004 — and cross-referencing it with ADHD diagnosis records — the study1 found that children born between September and December of each year were significantly more likely to be diagnosed with ADHD than were children born between January and April. Younger boys were 26 percent more likely to be diagnosed, while girls were 31 percent more likely.

The results suggest that a younger child’s perceived “immaturity” may influence his or her likelihood of an ADHD diagnosis, experts say. A younger child is developmentally more likely to be hyperactive or have difficulty focusing, making him or hr more likely to draw the attention of teachers or doctors. In many children, however, these “symptoms” don’t necessarily merit an ADHD diagnosis.

And while elementary-age children are developmentally more prone to hyperactivity, it’s not just young children who are at risk for a skewed diagnosis, the researchers said. Further analysis of the middle and high school years showed an even stronger association between birthdate and ADHD diagnosis.

To avoid missed or incorrect diagnoses, the researchers conclude, “Teachers, parents, and clinicians should take relative age into account when considering the possibility of ADHD in a child or when encountering a child with a pre-existing diagnosis.”

The study was published in October in The Lancet.


1 Sayal, Kapil, et al. “Relative Age Within the School Year and Diagnosis of Attention-Deficit Hyperactivity Disorder: A Nationwide Population-Based Study.” The Lancet, vol. 4, no. 11, 2017, pp. 868–875., doi:10.1016/s2215-0366(17)30394-2.

Updated on November 30, 2017

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