A major new study from Norway has found that children born later in the school year—those who are the youngest in their class—are significantly more likely to be diagnosed with mental health problems than their older classmates. The research, which analyzed data from over one million children, has ignited global debate over how education systems, including Thailand’s, may inadvertently disadvantage their youngest students through rigid school entry cut-off dates. Experts are now urging policymakers and educators to reconsider age-based class placements and provide additional support to mitigate these long-term mental health risks.
The Norwegian University of Science and Technology (NTNU) study, recently published in BMJ Pediatrics Open, tracked the mental health diagnoses of children aged 4 to 17, born between 1991 and 2012, using comprehensive national health registries. The research revealed that children with birthdays in October, November, or December—the last quarter of the year and typically the youngest in each school cohort—were more frequently diagnosed with attention deficit hyperactivity disorder (ADHD) and other neuropsychiatric disorders compared to peers born in the first quarter. The findings were consistent for both boys and girls, and for children born full-term as well as prematurely. Notably, the risk increase for ADHD diagnoses among the youngest class members ranged from 20-80% depending on gestational age, a striking figure in the context of childhood mental health (medicalxpress.com).
Lead researcher and Ph.D. fellow at NTNU’s Department of Public Health and Nursing described these results as a clear “relative age effect,” a concept recognized internationally but rarely addressed in school placement policies. “Our findings show that the youngest members of a school class tend to be diagnosed with a mental illness more frequently than the oldest,” noted the NTNU specialist, who also works as a neonatology consultant at St. Olavs Hospital. For children born prematurely, the risks appear compounded; the study found that premature girls born late in the year were especially likely to be diagnosed with emotional disorders like anxiety and depression compared to their older, also-premature peers.
Why does being the youngest in the classroom matter? The research suggests that differences in cognitive, emotional, and social maturity—often just a matter of months—make a significant impact on children’s ability to cope with academic and behavioral expectations. Younger children can appear less attentive, more impulsive, or less socially adept simply because they are less mature than their older classmates, not necessarily because of underlying pathology. This developmental gap might lead teachers, parents, and clinicians to interpret normal but immature behavior as signs of psychological disorders, resulting in increased—and potentially unnecessary—mental health diagnoses.
The NTNU team argues that the observed trend is “partly linked to the way in which we organize our education system.” While the study focused on Norway, international findings—including research in the US, UK, and Australia—have documented similar patterns, fueling concerns that age-based school entry rules could inadvertently shape a child’s educational trajectory and mental health outcomes (BMJ Pediatrics Open, Harvard Health, The Conversation).
For Thailand, where public and private schools commonly enforce a cutoff date for school entry (generally May or June), the issue is highly relevant. Just as in Norway, Thai children born in the months immediately before the cutoff are often the youngest in their cohort—sometimes up to 11 months younger than their oldest classmates. According to Thai educational psychologists, this age gap can generate disparities in academic performance, social integration, and even the likelihood of being identified with learning or behavioral disorders. “In a Thai classroom, a difference of a few months at age six or seven is developmentally substantial,” explained a senior consultant at a major Bangkok children’s hospital. “We see that younger students sometimes struggle not because they lack intelligence but because their maturity level is naturally lower than their classmates’.”
Thailand’s culture of high academic expectations, rote learning, and standardized testing may further exacerbate the issue. The youngest children must often compete in the same high-stakes environment without additional accommodations for their relative immaturity. Some studies suggest this can result in lower self-esteem, academic disengagement, and increased stress—factors which may persist into adolescence and early adulthood (see Bangkok Post, World Bank Education in Thailand ). In the NTNU study, the identification of increased risk for ADHD and other neuropsychiatric disorders among the youngest children echoes similar Thai findings regarding overdiagnosis and stigma in Thai school environments.
Globally, the “relative age effect” debate has led several countries to adjust their policies, such as allowing flexible school-start dates, optional grade repetition, or increased teacher training to recognize developmental differences. In Japanese and Finnish schools, for instance, educators are trained to avoid assuming that younger, more active children necessarily have attention disorders, recognizing instead a spectrum of normal development (World Economic Forum). The NTNU research team recommends that education systems consider more flexible entry procedures or targeted support for younger students to reduce unnecessary labeling and mental health referrals.
In Thailand, some progressive private schools have begun to experiment with developmental assessments for school entry, rather than strict adherence to cut-off dates. However, nationwide policy has yet to adapt to international research findings. An official from the Office of the Basic Education Commission, speaking on anonymity, acknowledged discussion of this issue, noting, “We are aware of international research suggesting flexible school entry may benefit some children. However, systemic changes require careful planning to align with existing laws and parental expectations.”
There is also a distinctive Thai cultural context to consider: traditionally, Thai families may place considerable value on earlier academic achievement, sometimes encouraging children to enter school as soon as eligible, regardless of their readiness. This practice, while intended to give children an early start, can magnify the developmental gap highlighted in the NTNU research. Experts warn that culturally sensitive education campaigns are needed to help parents and teachers recognize the importance of maturity—not just chronological age—in school placement.
Within Thai classrooms, teachers face competing demands. Large class sizes—often exceeding 40 students in public schools—make individualized attention and differentiated instruction challenging. Bangkok-based educators report that pressure to cover national curriculum and prepare students for exams leaves little time for accommodating wide developmental ranges. “The national exam system expects all children to be ready at the same time, which is not realistic given wide age and maturity differences,” a public school advisor observed (Thai Ministry of Education policy documents, UNICEF Thailand).
The NTNU report’s authors suggest possible solutions, including: permitting flexibility in school start age, providing transitional support for the youngest pupils, and training teachers to distinguish between normal age-related immaturity and genuine developmental concerns. In the Thai context, practical recommendations include piloting readiness assessments for school entry, offering catch-up programs for the youngest and least mature students, and increasing access to school psychologists who are trained to recognize the relative age effect. Some international experts have also suggested “redshirting”—voluntarily delaying school entry for younger children—as a possible option for families, though this can carry social and financial costs.
Looking forward, if Thailand were to adopt policy shifts informed by this growing body of research, several positive outcomes could result: fewer unnecessary mental health diagnoses, improved academic engagement for the youngest students, and a broader conceptualization of readiness for learning that respects each child’s developmental timetable. However, successful reform would necessitate coordinated action between policymakers, educators, parents, and mental health professionals—alongside sustained investment in training and resources.
For Thai families and educators, immediate steps include paying attention to children’s readiness and advocating for supports when a child seems to struggle, recognizing that age-related immaturity is not a disorder. Parents should consult with child development specialists or school counselors if they have concerns about their child’s adjustment, rather than assuming academic problems always require medical diagnoses. Teachers can benefit from professional development that equips them to recognize the spectrum of normal childhood development, and policymakers should prioritize pragmatic reforms that align with evidence from both Thai and international studies.
To read the original NTNU study summary, see the report at Medical Xpress. For the academic article, refer to BMJ Pediatrics Open and updates from the Norwegian University of Science and Technology. For context in the Thai educational system, consult resources from the Thai Ministry of Education, UNICEF Thailand, and the World Bank Education Monitor.