This is something I’ve known for some time now, often related to the relative age effect: Children born in December are almost twice as likely to be diagnosed with a learning disorder as those born in January.

But there is more…

From the press release:

Children born in December are almost twice as likely to be diagnosed with a learning disorder as those born in January. ADHD was found not to affect the association between month of birth and the likelihood of a learning disability diagnosis.

The new, register based study included children born in Finland between 1996 and 2002. Of nearly 400,000 children, 3,000 were diagnosed with a specific learning disorder, for example, in reading, writing or math by the age of ten.

“We were familiar with the effects of the relative age to the general school performance, but there were no previous studies on the association between clinically diagnosed specific learning disorders and relative age, which is why we wanted to study it,” says Doctoral Candidate, MD Bianca Arrhenius from the Centre for Child Psychiatry at the University of Turku, Finland.

In previous studies, children born later in the year, and therefore younger than their classroom peers, have been found to be at increased risk of psychiatric disorders, low academic achievement, and being bullied.

ADHD does not affect learning disabilities

Many children with learning disabilities are diagnosed with ADHD. The study compared children with both learning disability diagnosis and ADHD separately from children with learning disabilities but without ADHD, and ADHD was found not to affect the association between month of birth and the likelihood of a learning disability diagnosis.

“This finding was surprising. In children referred to specialist care, the problems are typically complex. We did not expect the impact of relative age on “pure” learning disorder to be so significant, given previous research findings on relative age to ADHD,” says Dr Arrhenius.

“Diagnosing learning disorders with psychological tests also takes the exact age of the child better into account compared with the methods used in diagnosing ADHD. For this reason, too, we expected more moderate differences between the months of birth. It seems that relatively young children are more easily sent to specialized health care,” Arrhenius ponders.

Aiming for equality

Research shows that teachers, health care personnel, and parents need to be aware of the phenomenon of relative age, especially when assessing a child’s learning ability.

“There is a risk of both over- and under-diagnosis, meaning that the youngest in the class are proportionately diagnosed so much more that the older students in the class may even be deprived of the diagnosis and rehabilitation they need. A more systematic screening for learning disabilities could be one approach that would even out the effect of relative age on referrals to specialized health care,” says Arrhenius.

Abstract of the study:

Background
Being among the youngest in class has previously been associated with attention‐deficit/hyperactivity disorder (ADHD) and academic disadvantage, but the relative age effect on learning disorders is less well understood. This study examined whether relatively young children are more likely to be diagnosed with specific learning disorders than their older peers.

Methods
The setting included all 388,650 children born singleton in Finland from 1996 to 2002. Cases diagnosed with specific learning disorders in specialized health care by the age of 10 were identified from national registers. Cumulative incidences of specific learning disorders and the corresponding incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were calculated for each birth month compared to January.

Results
During follow‐up, 3162 (0.8% of 388,650) children were diagnosed with a specific learning disorder. Children born in December displayed higher cumulative incidences for specific learning disorders than children born in January (IRR: 1.77, 95% CI: 1.50–2.11). The findings were similar for girls (IRR: 2.01, 1.44–2.83) and boys (IRR: 1.70, 1.39–2.08). ADHD did not explain the association, as the IRR for the youngest children with specific learning disorders and ADHD was 1.59 (1.13–2.26) compared to those without ADHD (IRR: 1.84, 1.51–2.24).

Conclusions
Relatively younger children in Finnish schools were more likely to be diagnosed with a specific learning disorder by the age of 10. Increased awareness of how relative age differences affect the likelihood for children to be diagnosed with specific learning disorders is needed among parents, clinicians, and teachers.