Children who are among the youngest in their school year have an increased chance of mental health problems, say doctors.
Being the youngest in the class is stressful for some
A study of more than 10,000 British children has found pupils who are younger than their classmates are more likely to have a psychiatric disorder.
Writing in the British Medical Journal, the researchers said the risks applied to students in primary and secondary school and maybe even at university.
They suggested teachers should make greater allowances for young children.
Professor Robert Goodman and colleagues at the Institute of Psychiatry in London surveyed 9,383 five to 15-year-olds in England and Wales.
They divided the children into three groups depending on their age in relation to the rest of their school class - oldest, middle and youngest.
They found that 8.3% of children in the oldest third of the class and 8.8% of children in the middle age range had a psychiatric disorder.
These include anxiety, depression, behavioural and emotional difficulties.
However, children in the youngest third had much higher rates - 9.9% of these had a psychiatric disorder.
The researchers also looked at students in Scotland.
In England and Wales, the oldest children in the school year are born in September while the youngest are born in August.
In Scotland, the oldest children are born in March and the youngest in February.
Nevertheless, the researchers reported similar findings in students north of the border.
This led them to conclude that the age of a child in relation to the rest of the class is the important factor, rather than time of year they are born.
The researchers said these risks could be reduced if teachers and schools made greater allowances for the youngest class members.
"Around 60,000 of these cases of child psychiatric disorder might be prevented if the youngest and middle children in a school year were at no more risk than the oldest children," they wrote.
"Several studies suggest that teachers often forget to make allowances for relative age, expecting too much of the younger children and being more likely to see them as failing."
They said teachers could remind themselves that not all children are at the same stage by taking steps like calling the register in birth order rather than alphabetically and grouping children together by age.
In addition, steps could be taken to reduce the stress on young children, they said.
"Streaming children according to their relative age within each year group may also be helpful, as may allowing children to repeat a year," they wrote.
The researchers also pointed to education policies in New Zealand, where children spend between one and two years in a preparatory class.
They are only moved up into the next class when teachers decide they are mature enough and are at the right academic level.
The National Union of Teachers said British teachers were aware of the differences between children.
"Teachers will know individuals extremely well," a spokeswoman told BBC News Online.
"They will know that child's strengths and weaknesses. They have lesson plans for the class as a whole but they will also have lesson plans geared to each child."
She added that schools can keep children back if they feel that they are not ready to progress.
"There is a facility in this country to hold children back and not to automatically move them up. There is flexibility. However, holding a child back can have an impact on that child and schools need to take that into account too."