Youngest in the class and diagnosed with ADHD? What the studies show

Every class has a spread of birthdays. In a Singapore Primary 1 class, a child born in January can be almost a year older than one born in December. In the US and UK, the youngest are usually summer babies. At six, that year is a big share of a child's life, and it shows in exactly the things teachers notice: sitting still, waiting a turn, following instructions. Two large studies have looked at what this does to ADHD diagnosis.

What the studies found

Nearly a million children in Canada

In British Columbia, children born in December are the youngest in their school year. Researchers followed 937,943 children aged 6 to 12. Boys born in December were 30% more likely to be diagnosed with ADHD than boys born in January, and girls born in December were 70% more likely. The youngest were also more likely to be prescribed ADHD medication: 41% more for boys and 77% more for girls (Morrow et al., 2012). The authors raised concerns about overdiagnosis.

Around 400,000 children in the US

Many US states require children to be 5 by 1 September to start kindergarten, so August babies are the youngest in their year. Using insurance records, researchers compared children born in August with those born in September. In states with the 1 September cut-off, ADHD was diagnosed in 85.1 per 10,000 August-born children against 63.6 per 10,000 September-born, roughly a third higher. In states with other cut-off dates, there was no such gap, and August and September babies did not differ on asthma, diabetes or obesity (Layton et al., 2018). That last check matters: it suggests the gap comes from school age, not from something about being born in summer.

Why it happens

ADHD is diagnosed partly from how a child behaves compared with others. The skills involved, like waiting, sitting through a lesson, and holding three instructions in mind, all grow with age. A child who is ten or eleven months younger than many classmates can look restless or inattentive next to them while being completely typical for their own age. Teachers compare children with the class in front of them; that's natural, and it's exactly where the bias can creep in.

What it doesn't mean

• It doesn't mean ADHD isn't real. ADHD is a real, well-studied condition, and diagnosis and support change many children's lives for the better.
• It doesn't mean a young child's diagnosis is wrong. Many youngest-in-class children do have ADHD. The studies show a pattern across hundreds of thousands of children, not a verdict on yours.
• It doesn't tell you about teenagers. The Canadian study looked at children aged 6 to 12, and the US study at children up to about 8.

What to do if you're worried, or the school is

1. Know the cut-off. Find out the month your child's school year starts, and where your child's birthday falls. In Singapore it is January to December; in England, September to August; in the US, it depends on the state.
2. Ask the fair question. "Compared with children born the same month, is this still unusual?" A good teacher or clinician will welcome it.
3. Look beyond the classroom. ADHD shows up across settings: home, school, clubs, playdates. A proper assessment gathers information from more than one place and asks how long the difficulties have lasted.
4. Watch over time. Some behaviour that worries a teacher at five settles by seven. Some doesn't. Both are useful to know.
5. Don't wait if things are hard. If your child is struggling, unhappy or falling behind, ask for help now. Being young for the year and having ADHD can both be true.

If ADHD is confirmed, it helps to understand what it is and isn't. Start with why ADHD kids aren't lazy, and how ADHD overlaps with dyslexia and autism.

For older students who just need help getting started on homework, our free Tiny steps tool breaks a task into one small step at a time, with a five-minute timer. No account needed. More study tools are on the Versed blog.

References

• Morrow, R. L., Garland, E. J., Wright, J. M., Maclure, M., Taylor, S., & Dormuth, C. R. (2012). Influence of relative age on diagnosis and treatment of attention-deficit/hyperactivity disorder in children. CMAJ, 184(7), 755-762.
• Layton, T. J., Barnett, M. L., Hicks, T. R., & Jena, A. B. (2018). Attention deficit-hyperactivity disorder and month of school enrollment. New England Journal of Medicine, 379(22), 2122-2130.