Schools may not be responsible for the static levels of social mobility in English education, according to a leading academic.
Instead, the enduring disparity between the average exam results of richer and poorer pupils may be explained by an often ignored alternative - the burgeoning out-of-school support now available to middle-class parents.
This includes access to private tutors, parenting classes, and even help with university applications - all of which come at a price.
The claim was made by Professor Stephen Ball, of the Institute of Education in London, during a speech reflecting on the 20 years of English education since the Education Reform Act of 1988.
His comments came as statistics revealed by the Conservatives last week showed a huge gap in GCSE results between some richer and poorer areas.
Professor Ball said: "There has been a fantastic growth under New Labour in the market for education 'peripherals'.
"Parents are able to spend money to supplement state schooling in a whole variety of ways to ensure the success of their children.
"If you want to understand education, in terms of the difference of performance (between pupils from different socio-economic backgrounds) looking solely at schools is the wrong thing to do.
"You have to look at what goes on outside of schools to understand how these differences are being maintained."
He then reeled off a host of services that he said were now being taken advantage of by a growing number of parents, many of whose children attend state schools.
For example, a company called Accelerated Learning offers parents - and schools - the chance to buy books, DVDs and online learning materials designed to boost understanding from pre-school to adult level.
Another firm, called The Parenting Practice, claims to "help you become a better parent", said Professor Ball.
He added: "For Pounds 220, you can have a one-to-one interview over the telephone with a parenting adviser who can sort out your problems while you are sitting at your desk at work."
There were also hundreds of tutoring companies. And, as The TES has reported, Sainsbury's and Tesco offer a service where parents can leave their five to 14-year-olds for tutoring in English and maths while they shop, charging them up to Pounds 98 a month.
At the other end of the age scale, firms help with applications to Oxbridge, including interviews. The links between socio-economic background and academic performance are well-established.
The Conservatives' figures showed that, in deprived Holme Wood in Bradford, West Yorkshire, only 3 per cent of teenagers achieved five good GCSEs, including English and maths. Meanwhile, in part of Richmond upon Thames, west London, the figure was 100 per cent.
Social mobility also appeared to have stalled, with a major study showing that children born in 1970 were more likely to be in the same earnings bracket as their parents than those born in 1958.
Professor Ball said understanding the trend for the middle classes to take greater advantage of private education services did not mean curtailing it. But the tendency needed to be acknowledged.
It was possible, he said, for the public sector and charities to try to replicate similar support for children from poorer homes - for example, through breakfast and after-school clubs. But the scale of the challenge needed to be recognised, he said.
He conceded that some policies, such as contextual value added league table measures, showed ministers were taking pupil background into account in policymaking.
But he added: "The massive weight of policy announcements by politicians is directed at schools, including the recent talk about hundreds of underperforming schools."
Jim Knight, page 35.