In 2003, 7.8 percent of children ages 4 to 17 were diagnosed with ADHD. In 2011, that number had jumped to 11 percent. The number for children ages 2 to 5 increased by more than 50 percent.
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The Harvard study looked at children in states with a strict Sept. 1 birthday cutoff policy for starting school. Researchers then compared 407,000 U.S. children born between 2007 and 2009 with August or September birthdays. The study followed those cases until 2015.
What they found was that children with August birthdays – who were the youngest in their classes – were 34 percent more likely to be diagnosed with ADHD than the children who were born only weeks, or in some instances only days later, in September.
“There’s no reason an August child and September child separated by just a couple weeks at birth would be any different. And yet, we found a big difference in diagnosis,” Harvard Medical School’s Anupam Jena, one of the authors of the study, told The Post.
The study didn't evaluate whether the children were diagnosed appropriately. The August-September difference could be a reflection of spotting actual cases of ADHD earlier in the August-born kids because of their early start to school, Dr. Jonathan Posner told The Associated Press.
Posner is an associate professor of psychiatry at Columbia University Medical Center in New York.
"The information we receive about a child has to be interpreted within a developmental context," Posner said. "A 4-year-old isn't going to respond as well to academic challenges as a 5-year-old."
A younger student may simply need time to catch up, Posner said, but that child’s immature behavior looks like ADHD and raises a teacher's concern. Posner wasn't involved in the study.
The study also found:
- That August-born students, especially the boys, are more likely to be on medications for ADHD and to take the drugs longer than the September-born children.
- That asthma, diabetes and obesity rates were the same for the August and September babies. And no other month-to-month comparison showed a sharp difference in ADHD.
- That states that don't use a Sept. 1 cutoff did not see the effect.
- The study released this week is not the only one to show a link between a diagnosis of ADHD and the age at which a child begins school.
A similar study showed that in addition to an early ADHD diagnosis, children born in August who start school months younger than their peers are more likely to drop out of school or be jailed for a juvenile crime.