Some children are diagnosed with ADHD — attention deficit hyperactivity disorder — when they are younger than and just less mature than their classmates, according to a new study from Iceland.

"Educators and health-care providers should take children's ages in relation to their (classmates) into account when evaluating academic performance and other criteria for ADHD diagnosis," said study author Helga Zoega, a postdoctoral fellow at Mount Sinai School of Medicine in New York City. "Parents can use these findings to help inform their decisions about school readiness for children born close to cutoff dates for school entry."

Researchers looked at the test scores of nearly 12,000 children born between 1994 and 1996 in Iceland, tracking those who were prescribed drugs for ADHD.

About 6 percent of the children — 740 — were prescribed medication to treat ADHD between 2003 and 2009. Those in the youngest third of their classes were 50 percent more likely than their peers in the oldest third to be prescribed ADHD drugs from ages 7 to 14, the study found.

"In the education system, it leads to the question, 'What strategies or resources do we need to help ensure the well-being of all children in the classroom, where children vary in age by up to a year?’ ” Richard Morrow, a health research analyst at the University of British Columbia who studies ADHD, told U.S. News. "Parents need to be aware that if behavioral issues arise for their child, this may be related to their child's relative age in the classroom."

The authors cautioned that such measures may not fully predict long-term psychiatric and academic outcomes, ABC News reported. "Nor could the study rule out possible undertreatment of ADHD in the oldest kids as the mechanism rather than overtreatment in the youngest, the investigators noted."

Rachel Lowry is a reporter intern for the Deseret News. She has lived in London and is an English graduate from Brigham Young University. Contact her at or visit