Middle class children who attend state schools with average results, or worse, still do well because of their backgrounds, a study suggests.
The schools were chosen because they were socially diverse
Most children from the 124 families studied also did well at GCSE, with up to 15% going on to Oxbridge.
The study said parents deliberately picked socially diverse schools, believing the experience would help their children become better citizens.
But it found most of the children did not mix much with other social groups.
Researchers from the Universities of Cambridge, Sunderland and the West of England (UWE) carried out 248 in-depth interviews with the parents and children who had made "counter-intuitive school choices" in London, north and south England.
They had picked a state comprehensive performing at or below the England average for GCSE results as a positive choice.
Professor David James of the UWE said: "Lots of middle class people move house, decide to pay for private education, rediscover religious allegiances or even rent a new address to get the secondary schooling that the market appears to hold up as ‘best'.
"But we wanted to discover what motivates parents who instead choose to send their children to local comprehensives that appear to be performing poorly on the conventional measure."
He added: "Most children who have had this choice made for them by the parents taking part in this study have gone on to perform brilliantly in GSCEs, A-levels and then on to university entrance, including a much higher than average entry to Oxbridge."
However, the majority of those studied acknowledged that they could or would "pull out" if things did not go well.
At one end of the spectrum were parents who were confident that their child would do well wherever they went to school.
At the other, were highly anxious parents who felt compelled to micro-mange their child's school experience.
But the study found that far from encouraging social mixing, most children stuck with their middle class friends.
And middle class pupils dominated the top sets and gifted and talented lists that were given extra help.
This raised the issue of whether middle class pupils were taking resources away from those from lower social groups.
Many of their parents were also heavily involved with the school, with many of them becoming school governors.
Professor Gill Crozier of the University of Sunderland said: "The children often get special attention as they are nurtured by teachers who are keen to give extra help to improve the school's results."
The researchers said the net effect of the school choice was "consolidation of their middle class identity and a confirmation of their advantaged social position relative to other groups".
Prof James said schools were doing their best job in difficult circumstances.
But because the local education market was driven by league table positions, schools often chose to prioritise resources on those most likely to succeed - i.e. those with more stable emotional and social backgrounds.
The report follows a raft of research papers which suggest middle class parents dominate good, state schools because they can often afford the higher house prices close to them and know how to work the admissions system.