The most successful state secondary schools in England are admitting too few children from poorer families, says a report from an education charity.
Successful schools are dominated by better-off families, says research
The Sutton Trust says that in the top 200 schools, only 3% of pupils qualify for free school meals - compared to a national average of 14%.
"The best comprehensives serve the relatively affluent," says the Trust's chairman, Sir Peter Lampl.
He called for a "network of school buses" to give schools a wider reach.
The research looked at the intakes of the 6% of state schools with the best results at GCSE - and found that poorer pupils were under-represented.
The majority of this sample of schools were grammar schools - but the researchers say that the social make-up of the top comprehensives and grammars were not dissimilar.
Even allowing for the better-off areas served by some of these schools, the report says that poorer pupils (as defined by qualifying for free school meals) were still under-represented.
"We have replaced an education system which selected on ability with one that is socially selective: the best comprehensives serve the relatively affluent, while the remaining grammar schools attract far too few able students from poor backgrounds," said Sir Peter.
He proposed that successful schools could develop outreach projects and that school transport should put schools into the reach of families without cars.
The report concluded that it is "clear that the admissions system is not operating equitably and is in need of review".
Later this month the government is expected to publish a White Paper which will address the question of how a wider range of pupils can gain access to successful state schools.
This could include plans to use school transport to put more schools in reach of poorer families.
There has been speculation that it could also extend using entry systems such as banding, in which schools are required to take pupils from all ability bands.
At present, where living close to the school is the main entry requirement, there have been accusations of "selection by estate agent" - where being able to afford a house in the right area determines access to the best schools.
"For too long, access to some schools has only been open to those who could afford to buy an expensive house next to a good school, while the rest were told to accept what they'd been given," the Education Secretary Ruth Kelly told the Labour party conference last month.