Summary: A global review finds that the youngest children in a classroom are more likely than their older classmates to receive an ADHD diagnosis. Researchers warn that teachers and clinicians may sometimes interpret normal age-related immaturity as symptoms of ADHD, leading to misdiagnosis and unnecessary medication.
Source: University of Adelaide.
Children who are youngest in their school year face a higher likelihood of being diagnosed with Attention Deficit Hyperactivity Disorder (ADHD) and of receiving medication than older classmates, according to a large international review involving the University of Adelaide.
The systematic review, led by Curtin University and published in the Journal of Child Psychology and Psychiatry, examined studies that compared a child’s relative age within a classroom to their chances of being diagnosed with or medicated for ADHD. The authors assessed evidence from multiple countries to identify whether a consistent “late birthdate” or relative-age effect exists.
Across the primary studies analyzed, researchers found a clear and widespread pattern: in many jurisdictions the youngest children in a school year were more frequently diagnosed and treated for ADHD than their older peers. The review included studies conducted in the United States, Spain, Canada, Finland, Germany, the Netherlands, Iceland, Israel, Norway, Sweden, Taiwan and Australia, among others, totaling millions of children.
Professor Jon Jureidini, a child and adolescent psychiatrist at the University of Adelaide and co-author of the review, emphasized the practical implications. He noted that teachers, parents and clinicians should recognize how relative age can shape behaviour and assessments. “A child who is younger and therefore less mature than classmates can appear inattentive or impulsive in comparison, even when their development is normal for their age,” Professor Jureidini said. “If we mistake that immaturity for ADHD, children can be put on medications they don’t need while the real causes of their difficulties remain unaddressed.”
Lead author Dr Martin Whitely, a research fellow at the John Curtin Institute of Public Policy, explained that ADHD diagnosis relies heavily on behavioral reports rather than biological tests. Because teachers are often the first to raise concerns about a child’s behaviour, differences in maturity among children in the same classroom can influence those reports. “Our review suggests that, in many countries, teachers’ observations contribute to a pattern where the youngest in the class are disproportionately labelled with ADHD,” Dr Whitely said.
The review found the late birthdate effect in both countries known for higher prescribing rates (such as the United States, Canada and Iceland) and in places with lower prescribing rates (including Finland, Sweden and Taiwan). This pattern challenges the assumption that higher medication rates alone explain misdiagnosis; instead, relative age appears to be an independent factor influencing diagnostic decisions internationally.
There were exceptions. Two Danish studies showed a weaker or absent late birthdate effect. The authors suggest this may be related to a common practice in Denmark known as “redshirting,” where parents delay school entry for children they feel are not ready. When many younger children are held back a year, the relative-age differences within a classroom are reduced, which could mask or prevent the late-birthdate effect. The review calls for further research to determine whether delayed entry mitigates risks for some children while possibly disadvantaging others.
The authors note several broader concerns about diagnostic practice. Symptoms that overlap with ADHD—such as sleep deprivation, bullying, trauma or social difficulties—can lead to an ADHD label when the root causes are not fully explored. Mislabeling a child’s behaviour as ADHD can result in unnecessary medication and can divert attention from addressing underlying problems.
The systematic review was led by researchers at the John Curtin Institute of Public Policy at Curtin University and involved collaborators from the University of Adelaide and other international institutions. Co-authors include experts in psychiatry and public health who contributed to the analysis and interpretation of findings from multiple countries.
Source: Jon Jureidini – University of Adelaide
Publisher: NeuroscienceNews.com (organized report)
Image source: Image in the public domain.
Original research: The review is titled “Attention deficit hyperactivity disorder late birthdate effect common in both high and low prescribing international jurisdictions: systematic review.” The study was authored by Martin Whitely, Melissa Raven, Sami Timimi, Jon Jureidini, John Phillimore, Jonathan Leo, Joanna Moncrieff, and Patrick Landman and was published in the Journal of Child Psychology and Psychiatry. DOI: 10.1111/jcpp.12991.
Suggested citation formats (no links):
MLA: University of Adelaide. “Youngest in Class More Likely to be Diagnosed with ADHD.” NeuroscienceNews. 15 October 2018.
APA: University of Adelaide (2018, October 15). Youngest in Class More Likely to be Diagnosed with ADHD. NeuroscienceNews.
Chicago: University of Adelaide. “Youngest in Class More Likely to be Diagnosed with ADHD.” NeuroscienceNews. Accessed October 15, 2018.
Abstract
Attention deficit hyperactivity disorder late birthdate effect common in both high and low prescribing international jurisdictions: systematic review
Background: Several studies have reported that the youngest children in a school year face a higher risk of being diagnosed with or medicated for ADHD. This systematic review investigated whether this late birthdate effect is widespread and whether its strength corresponds to overall diagnosis or medication rates.
Methods: The authors searched PubMed and ERIC, and conducted snowball and grey literature searches to identify relevant studies.
Results: The review identified multiple studies from more than a dozen countries, encompassing millions of children. The majority of primary studies (most of which reported data from over 14 million children in earlier summaries, and accounting for up to 15.4 million in included datasets) found that the youngest children in a school year were significantly more likely to be diagnosed with or medicated for ADHD. Two studies from Denmark reported a weaker or absent effect, possibly related to the common practice of delayed school entry for children judged by parents to be immature.
Conclusions: Internationally, relative age within a classroom is commonly associated with increased rates of ADHD diagnosis and medication for the youngest children. The presence of strong effects in countries with both high and low prescribing rates suggests that low national medication rates do not automatically indicate accurate or unbiased diagnostic practices. Further research is needed to explore whether policies such as flexible school entry reduce misdiagnosis or shift risks in other ways.