Children born in the summer struggle for years at school as they are put at a "clear and long-term disadvantage in the education system", according to a major review.
They are more likely to play truant and even commit suicide when they grow up after falling behind older classmates.
Pupils with birthdays in June, July and August are also less likely to succeed in sport and become professional athletes.
It comes amid debate over the best way to educate summer-born children.
In December, an interim review of primary education proposed bringing the recommended school starting age forward from five to four in England.
Experts said it would give children longer to master the basics of communication, although those with summer birthdays may be able to start part-time to acclimatise to the classroom.
But the latest study - by the exam board Cambridge Assessment - said it could make things worse.
It said younger pupils were not disadvantaged in countries such as Denmark and Finland, where children start school aged six and seven, respectively, and suggested England should follow.
Tim Oates, Cambridge's director of research, said: "Leaping into inadequately researched remedies could exacerbate rather than remedy this problem within our system."
The conclusions have been submitted to the on-going primary review, which is being led by Sir Jim Rose, former head of inspections at Ofsted.
In the report, academics considered evidence from 78 studies, dating back to 1953.
It cited a large-scale study of performance by seven-year-olds in national tests. Eight out of 10 girls born in September reached the Government's expected standard, compared to just 53 per cent among those born in August, researchers said.
The differences became less marked as children got older, but they were still "significant" in secondary school, said the study.
August-born children were slightly less likely than those with September birthdays to get good grades in the core subjects of English, maths and science at GCSE.
And September-born students were 20 per cent more likely to go to university.
The research also cited evidence that younger children had poorer school attendance records than their peers.
It quotes an American study, which examined the birth dates of under 20s who committed suicide in the US between 1979 and 1992. People who had been young for their school year were disproportionately represented in the figures. The study said the suicides could be the result of poor academic performance and low self-esteem.
The Cambridge research, led by Dr Liz Sykes, also looked at studies on the effects of birth date on athletic performance around the world, and found that those who were old for their year group tended to be the most successful.
Professional football clubs in England and the Netherlands had far higher numbers of players born in the autumn months than in the summer, and the same pattern was observed in Dutch youth tennis leagues and in Canadian ice hockey sides.
In gymnastics, where "physical maturation" is seen as a disadvantage, those who were young for their year dominated.
In response to the reserarch, Sir Jim denied all children should start school at four, but said it should "become the norm".
He added: "I will look at what Cambridge Assessment have got to say, and I will take it into account. But I cannot really say which way it is likely to push us." (By Warwick Mansell and Graeme Paton Last Updated: 4:00PM GMT 13 Feb 2009)