Children born later in the calendar year—particularly in October, November, or December—are at a higher risk of developing mental health disorders compared to their older classmates, a large-scale Norwegian study has revealed.
Researchers from the Norwegian University of Science and Technology (NTNU) analyzed health data from over one million individuals aged 4 to 17, all born between 1991 and 2012.
Their findings, published in BMJ Paediatrics Open, highlight what experts call “relative age effects,” where younger children in a school year cohort show increased vulnerability to emotional, behavioral, and developmental disorders.
The study found that children born late in the year were more likely to be diagnosed with mental health conditions such as anxiety, depression, and attention-related issues. These risks were consistent across both boys and girls, regardless of whether they were born full-term or prematurely.
Further concern was raised for the youngest girls born prematurely. This group showed a significantly higher risk for emotional disorders—particularly anxiety, depression, and adjustment disorders—when compared with their older preterm peers.
“These results underscore a critical concern in how educational systems may unintentionally exacerbate health disparities,” said Dr. Christine Strand Bachmann, a researcher at NTNU and consultant at St. Olavs Hospital’s Department of Neonatal and Adolescent Medicine. “The youngest students may display behaviors that are developmentally normal but are misinterpreted as clinical issues due to their relative immaturity.”
The findings suggest a need for policy reform in educational structures. Potential interventions include allowing flexible school start dates and offering enhanced support for the youngest and most developmentally vulnerable children.
In light of this evidence, the study calls on educators, healthcare professionals, and policymakers to reconsider how age-based school placement may influence long-term mental health outcomes in children.
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