The earlier a child starts kindergarten, the more likely he or she will be diagnosed with attention deficit hyperactivity disorder. That’s the conclusion of Harvard Medical School researchers, who recently published their findings in The New England Journal of Medicine.
The researchers analyzed records of more than 71,000 children with August and September birthdays in 18 states that had a school enrollment cutoffs date of Sept. 1. Children who turn 5 years old by that date can start kindergarten. Otherwise, they have to wait another year. That makes children with August birthdays the youngest in class, whereas those born in September are the oldest. Some 6 million children in the United States have been diagnosed with ADHD, which causes hyperactivity and inattention.
Researchers found the rate of ADHD cases was one-third higher among children born in August compared with those born in September. When they sampled more broadly to include insurance data for more than 400,000 children in states that don’t have a Sept. 1 enrollment cutoff, the disparity in ADHD diagnoses vanished.
Among other things, the researchers wanted to address a long-standing question among parents and experts: Should a child be held back from kindergarten an additional year? The answer, the researchers concluded, is nuanced. Parents consider a child’s age but also his or her relative maturity.
The study also found younger students are more likely to be put on and kept on ADHD medications than older children.
For parents thinking about a child’s school starting age, context is important: There’s no lab test for ADHD, and what looks like a disorder might just be immaturity.