Children born in the summer are already at a massive disadvantage by the end of their first year at school compared with older children, official figures reveal.
Almost two thirds of those born between May and August fail to meet minimum expected levels in areas such as reading, writing, speaking, maths and listening.
But little more than a third fall behind if their birthday falls between September and December.
The findings, from Department for Education data, reveal that children who are young for their year typically do worse at GCSEs and are less likely to get into university.
As the dad of both September and August-born boys, I would love to say: "What nonsense."
I'd love to contradict it and say that my September lad (aged nine) is distinctly average and my summer son (aged six) is top of the class. But that's not the case.
September Boy is pretty much top of his Year 4 class. He's top in maths, is brilliant at reading and is very level-headed and quietly confident.
Summer Son, though, is as daft as a brush. Compared to his older Year 2 peers, he can barely string a sentence together and is still counting on his fingers, where his classmates are doing three, four and six times tables in their heads.
And, yes, I worry about him – except for one thing: he is wonderfully creative, massively confident, and supremely popular amongst his peers. OK, he can't read (very well) and write (legibly) – yet – but he will, I'm sure.
On the other hand, September Boy isn't nearly challenged enough in his school. I try to fill in the gaps at home, but I'm not a teacher, and I believe he needs more academic stimulation at school.
In other words, it seems like he and the older members of the class are held back, waiting for the summer-born kids to catch up. It feels like no-one wins, but summer kids fare worst in the long run.
So what can be done about it?
A spokesman for the Department for Education, which compiled the latest study, said: "We have changed the Schools Admission Code to make it easier for summer-born children to defer their child's entry or request they attend part-time until they reach their fifth birthday.
"Schools should make this clear in their own admissions arrangements so that parents are fully aware of the options available for their children.
"Parents of summer-born children also have the flexibility to request their child enters reception class rather than Year 1."
The latest figures show that 49 per cent of children reached expected levels, rising to 60 per cent among autumn-born pupils. Among younger children it was 38 per cent.
However,the DfE report noted a significant gulf in academic areas but less of a difference in non-academic areas such as the ability to make friends.
He said: "Month of birth has the largest impact on the literacy and mathematics areas of learning.
"In contrast, gaps were narrower between autumn-born and summer-born children in health and self-care and making relationships."
Former chief inspector of schools Sir Mike Tomlinson, said: "We cannot expect that all learners achieve at the same rate. Indeed, there has been a plethora written about the disadvantages of summer babies, who statistically achieve lower marks than their peers, some of whom could be more than 11 months older."
More on Parentdish: Should child born prematurely start school a year later?
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