By Lisa Rapaport

Kids who are younger than most of their classmates may be more likely to be diagnosed with learning disabilities, depression, and attention deficit hyperactivity disorder (ADHD) than older students in their grade, a U.K. study suggests.

Researchers examined data from school enrollment and electronic health records for more than 1 million students ages 4 to 15. They calculated kids’ ages relative to their classmates based on their date of birth and the cutoff date for school enrollment where they lived.

Compared to kids who were the oldest in their grades, the youngest students – with birthdays within the final 3 months before the enrollment cutoff for their grade – were more than 30% more likely to be diagnosed with an intellectual disability, depression, or ADHD.

“We did not set out to determine the reasons for these links in our study and further research into the causes is needed, but there are a number of potential reasons,” said Jeremy Brown, a co-author of the study and researcher at the London School of Hygiene and Tropical Medicine.

“Younger children may find it harder to concentrate in class, leading to increased diagnosis of hyperactivity,” Brown said by email. “Issues such as inferior academic performance and poorer peer relationships can lead to mental health problems.”

In the study, researchers sorted students for each grade into 4 groups, from oldest to youngest. The oldest students had birthdays in the first 3 months of enrollment eligibility, while the youngest kids had birthdays in the final 3 months before the enrollment cutoff for their grade.

Roughly 800,000 children start primary school in the U.K. each year, Brown said. Diagnoses of intellectual disabilities, depression, and ADHD are relatively rare, he said.

The youngest kids were 30% more likely to have an intellectual disability than the oldest kids, researchers report in JAMA Pediatrics. That translates into roughly 2,100 of the youngest students getting diagnosed with an intellectual disability each year, compared with about 1,600 of the oldest kids, Brown said.

ADHD was diagnosed 36% more often among the youngest kids than the oldest kids. That translates into about 3,500 of the oldest kids and 4,700 of the youngest students getting an ADHD diagnosis each year, Brown said.

And the youngest children were 31% more likely to be diagnosed with depression than the oldest students. That translates into 2,200 of the youngest kids and 1,700 of the oldest kids getting a depression diagnosis each year, Brown said.

As Brown noted, the study wasn’t designed to prove whether or how students’ ages relative to their classmates might directly cause intellectual disabilities, depression or ADHD. And obviously, no matter what, every class will have an oldest and youngest student.

“Further research into effective interventions to minimize the impact of age in the school year is needed,” Brown said.

“Increased recognition of the issue among teachers, clinicians and parents might help. Additional support for children, such as from mental health services, may be of value,” Brown added. “In addition, a fairer and clearer process for deferring school entry for relatively young and developmentally immature children may be of benefit.”

SOURCE: JAMA Pediatrics, online September 23, 2019.