State school students do not outperform their peers from the independent sector once they get to university, new research has found.
The report from Cambridge University appears to contradict previous studies, which found that, on average, students from the state sector achieve better degrees than those from similar backgrounds who were privately educated.
The study's author, Richard Partington, found that among Cambridge students who began their studies between 2006 and 2009, there was no discernible difference between the average performance of students who attended state and independent schools.
The report comes as Prime Minister David Cameron attacked Oxford University for the low number of "black" entrants it admitted.
Mr Partington, senior tutor at Churchill College, said his research vindicated Cambridge's move to focus on students' GCSE and A-level grades and marks rather than interview performance.
"It makes theoretical sense for someone who's had a difficult education who has got good grades to perform better than one from a private background.
"But this shows we were right in the approach we have taken at Cambridge admissions in looking at exam results in great detail, not just at overall grades."
A study by the Sutton Trust, published in December, concluded that comprehensive pupils were likely to achieve higher degrees than independent and grammar school students with similar A-levels and GCSE results.
At the time, trust chairman Sir Peter Lampl said this confirmed that "universities are right to take into account the educational context of students when deciding whom to admit".
And a 2010 report from the London School of Economics' Centre for Economic Performance found state students were 4 per cent more likely to get a first or 2:1.
A Bristol University study, also published last year, found 3 per cent more state school students were awarded first-class degrees than their independent peers.
But the Cambridge study found that A-level performance was "overwhelmingly" the best guide to what class of degree an undergraduate would achieve, while gender "did not make a significant difference".
The overall performance of the school attended also had no bearing on what degree class they received.
"Admissions decisions are made on the basis of students' ability, commitment and potential," Mr Partington said.
Bernard Trafford, former chairman of the Headmasters' and Headmistresses' Conference, said: "I had a feeling there'd been rather more assertion than proof in previous research into this, from people with an axe to grind.
"There have been suggestions that we prep people before interview and they overperform. Of course we prep them; that's what parents pay for. But good university selection should be about judging potential."