The risk of Norwegian children receiving an ADHD diagnosis is higher for those born late in the year – after summer vacation. (Photo: Shutterstock / NTB scanpix)
The risk of Norwegian children receiving an ADHD diagnosis is higher for those born late in the year – after summer vacation. (Photo: Shutterstock / NTB scanpix)

More ADHD among December’s kids

Children born at the end of the year are statistically more likely to end up with an ADHD diagnosis than those born early in the year. Medical scientists are uncertain why.

Researchers at the Norwegian Institute of Public Health have studied the statistics on Attention Deficiency Hyperactive Disorder (ADHD) diagnoses among 510,000 Norwegian children aged six to 14. 

“There is a considerable difference both in the diagnosing and medication of ADHD between those born early in the year and those born towards year’s end,” says Kari Furu.

Furu is a researcher at the Norwegian Institute of Public Health and along with colleagues has recently published a study on this trend in the Scandinavian Journal of Public Health.

Fewer children with ADHD born before summer vacation

Higher shares of the kids born in late autumn and December received ADHD diagnoses. Children born from July to September were the cohort with the second largest likelihood of receiving the behavioural disorder diagnosis.

Proportionally far fewer children born in the first half of the year were given the diagnosis. Nearly no difference was seen in hazard ratios between January, February and March children and those who were born from April to June the same year.

“Why this could be, we don’t know,” says Kari Furu.

The same pattern is found regarding which kids were medicated for ADHD, according to the Scandinavian Journal of Public Health article.

The children included in the study were born from 1998 to 2006.

Largest difference among boys

This relationship to month of birth lasted throughout childhood and medication was not reduced as years went by, but in fact was increased during adolescence.

Boys born late in the year ran a 40 percent greater risk of being prescribed ADHD medications than those born early in the year.

Of course, such prescriptions are only given after a diagnosis is made.

“The number who received such medications increased with later months of birth,” says Furu.

By ninth grade, 3.6 percent of boys born between January and March were using ADHD medications.

Among ninth grade boys born from October through December, a total of 5.1 percent were getting such medication.

The same pattern was seen amongst girls, but the differences linked to their months of birth were less distinct.

As for girls in ninth grade born from in the first quarter, 1.1 percent were prescribed ADHD medicine, as against 2,1 percent of girls born in the last quarter.

Differences increase with age

This was the first time the link to birth months was shown in Norway. Studies from other countries have indicated the same phenomenon.

This study was novel because the researchers followed the children with the passage of time and found that the differences linked to birth months increased as the kids grew older.

The dissimilarity in numbers receiving medication linked to birthday months does not even out as the children age. On the contrary.

“This appears to intensify through the school grades,” says Furu.

Starting school as 6-year-olds

Furu points out that there are no reasons to believe that children born late in the year are more strongly biologically disposed for ADHD or exposed to special relevant environmental factors as compared to other children.

However, it is known that there are sizeable differences in the maturity of brain development amongst six-year-olds.

“So there can be variations in how much the children born late in the year, and are not six yet, can sit still and subject themselves to the school rules,” says Furu.

The Norwegian Directorate of Health’s guidelines for diagnosing ADHD in children point out that symptoms of inattentiveness, hyperactivity and impulsiveness should be clearly more evident than expected for a child of its age.

This means that the decision to refer a child to the specialist health services for examinations and a prospective diagnosis is partly based on evaluations of the child’s behaviour and performance as compared to children in the same class who were born months earlier.

Thus, the researchers deem it conceivable that the relative immaturity of the kids born late in the year is reflected in the outcome.

Do schools produce afflictions?

In 1997 a major educational reform was launched in Norway, starting kids off a year earlier. First grade began in the year a child turned six, rather than seven.

Has the start of school at age six some of the blame for these differences in diagnoses?

“We lack a basis of comparison and cannot say how this was before the reform was initiated with school starting a year earlier. Unfortunately, we don’t have a patient register with information on diagnoses on an individual level prior to 2008,” informs Furu.

Thus, they cannot compare the distribution of ADHD diagnoses in the years before the reform, when kids started school in the same year they turned seven.

Aksel Tjora, who has published a book on ADHD, comments the study in the same edition of the journal. He is a professor at the Department of Sociology and Political Science at the Norwegian University of Science and Technology (NTNU).

He considers the study very robust and thinks it goes fairly far in indicating that schools are producing afflicted children. Tjora thinks much of the increase in ADHD diagnoses is actually a pedagogical challenge that is disguised as a diagnosis. He points out that the symptoms of impulsiveness, hyperactivity and lack of concentration are predominantly problems in a school classroom situation.

“This occurs when health personnel start diagnosing social problems as a disorder that can be medicated,” he says.

Freeing parents and teachers

“From a pure sociological stance, one could query why a fraction of the least mature children are responding to teaching in a way that is defined as deviant,” he says. 

An ADHD diagnosis can sometimes be a relief for parents as well as teachers, because the problem is identified.

“In this way, what might be pedagogical challenges in the classroom get individualised,” suggests Tjora.

Tjora thinks that ADHD diagnostics and medications of inattentive and restless kids simultaneously exempts the school system from the responsibility for matching teaching conditions to the needs of the youngest children.

He thinks the problem becomes un-politicised. A single version of human behaviour gets defined as the norm. The responsibility for social deviation is individualised and the solution becomes individual treatment.

“The school start for six-year-olds was originally supposed to be a gentle transition, with lots of play time and physical activity. But in the last few years there’s been more emphasis on arithmetic, reading and writing,” says Tjora. 

Denmark with fewer differences

Danish researchers have conducted a similar study and also found distinctions in the share of diagnoses linked to month of birth.

“But there the association is much weaker than in our study,” says Furu.

She adds, however, that while the trend linked to month of birth is weaker in Denmark than in Norway, the overall share of children who are given the diagnosis in the two countries is quite similar.

Tjora is glad that the study steers focus away from biological and psychiatric explanations for the diagnosis. A previous study has also shown large differences in relative shares of ADHD diagnoses between Norwegian counties. Tjora calls for more research regarding whether using different educational models and methods or other ways of organising schools can be factored in. 

He thinks a solution could be a more flexible school start, as the case is in Denmark.

“One might also try to arrange school classes in different ways, for instance according to birth months,” says the professor.


Read the Norwegian version of this article at

Translated by: Glenn Ostling

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