The plight of summer-born children is well documented: those who are young in their year group struggle to keep pace with older classmates and perform less well in end-of-year tests.
But major research published today reveals that students who are young for their year are almost twice as likely to be identified as having special educational needs.
Children in England born in August are also marginally less likely to get a degree than their peers born in September at the start of the school year, less likely to have confidence in their abilities and less likely to believe that they can shape their own futures.
The findings, from the Institute for Fiscal Studies (IFS) thinktank and funded by the Nuffield Foundation charitable trust, are based on an analysis of 48,500 children in England, although similar patterns have been found in other countries.
The problem calls for radical solutions, with researchers recommending that national test scores be adjusted for age. These revised marks should then be used to determine positions in school league tables and admissions to higher education.
"Our findings point to a simple solution to the pitfalls of testing children born at the start and end of the academic year at very different ages," said Ellen Greaves, research economist at IFS and the author of the report.
"Age-adjusting the cut-offs required for pupils to achieve particular grades would ensure that no child is prevented from going on to further or higher education simply because of the month in which they were born."
The effects of being summer-born do not have a lasting impact into adulthood, the researchers found: employment prospects and earning potential are unaffected. But at school the differences are stark: 12.5 per cent of August-born children are labelled at age 11 as having mild special educational needs, compared with 7.1 per cent of those born in September. They are also 1 percentage point less likely to have obtained a degree.
Researchers say these differences are largely because these children are the youngest in their school year rather than because of the age at which they started school or how much education they have had.
They recommend that age-adjusted scores should be produced and used for school accountability and access to further and higher education, but that on leaving education students should also receive non-adjusted grades to show the absolute standards they have reached.
"Children may be held back (to the year below) for an underlying reason but holding children back simply because they are young doesn't solve the overall problem," Ms Greaves said. "As soon as you allow some parents to delay entry you are still left with other children who will be younger in the year."
Andrew Carter, headteacher of South Farnham School for children aged 4-11 in Surrey, southeast England, uses age-adjusted tests to assess children's reading ability and IQ.
"If an eight-year-old is in a running race against a 10-year-old, we're not shocked if the eight-year-old doesn't run as fast," he said. "By 14 it makes less difference. It's the same with intellect.
"What we need to understand is whether we are pushing children forward at a reasonable rate. There are various factors that are linked to children's progress, whether they are summer-born, boys, claim free school meals or have a disadvantaged background. We don't want it to become self-perpetuating that if you are summer-born you will always do a little less.
"If a child is summer-born it is worth asking whether that is affecting their attainment and the standardised tests are very useful in helping us to answer that question."
THE BIG KID BOON
Politicians in the US Senate and House of Representatives are up to 50 per cent more likely to have been one of the oldest in their class at school than the average person, according to researchers from Queensland University of Technology in Australia.
The bias in birthdays seems to be linked to a "multiplier" effect of doing well early on, the researchers said.
They added that children who are the oldest in their year group benefit from learning leadership skills early in life.