Kids born in August are diagnosed with ADHD more than kids born in September

Children who turn 5 just before starting kindergarten are much more likely to be diagnosed with attention-deficit/hyperactivity disorder than their oldest classmates. The finding bolsters concerns that the common neurodevelopmental disorder may be overdiagnosed.

“We think … it’s the relative age and the relative immaturity of the August-born children in any given class that increases the likelihood that they’re diagnosed as having ADHD,” says Anupam Jena, a physician and economist at Harvard Medical School.

Jena and his colleagues analyzed insurance claims data for more than 407,000 children born from 2007 through 2009. In states that require kids be 5 years old by September 1 to begin kindergarten, children born in August were 34 percent more likely to be diagnosed with ADHD than those born nearly a year earlier in September — just after the cutoff date. For August kids, 85.1 per 10,000 children were diagnosed with ADHD, compared with 63.6 per 10,000 for the September kids, the researchers report in the Nov. 29 New England Journal of Medicine.

People with ADHD typically have symptoms of inattention, hyperactivity and impulsiveness that are severe or frequent enough to interfere with their daily lives. In 2011, 11 percent of U.S. children aged 4 to 17 were reported to have an ADHD diagnosis, a rate higher than most other countries. Differences between states also suggest overdiagnosis, says Jena, “unless there’s something so different about kids across different states.” For example, while nearly 19 percent of 4- to 17-year-olds reportedly were diagnosed in Kentucky, the rate was about 12 percent in neighboring West Virginia.

“Greater recognition of ADHD is a good thing,” as the condition can lead to lower academic achievement, poor social skills and substance abuse, says Stephen Hinshaw, a clinical and developmental psychologist at the University of California, Berkeley, not involved with the study. But a brief office visit may result in an inaccurate diagnosis, he says, if other factors or conditions aren’t ruled out.

“Children mature at different rates,” Hinshaw says. Many issues in childhood, from anxiety to dealing with overcrowded classrooms, may resemble ADHD.

“We don’t want to overreact to inattention, lack of focus, impulsive behavior and large amounts of overactivity,” he says. “We need to understand the child’s other skills.”