Social class, more than sex or ethnicity, remains the strongest predictor of academic achievement in Britain, according to a new study by two influential academics.

Emma Perry and Becky Francis, of think-tank and charity the RSA, carried out a major review of research into the effect of social class on pupils’ education.

The current education system, driven by league tables and market forces, only exacerbates the gap between working-class and middle-class pupils, they said.

At key stage 2, 53.5 per cent of pupils eligible for free school meals reach the expected level 4 in English and maths. By contrast, 75.5 per cent of other pupils reach this level.

And only 4 per cent of those eligible for free school meals at the age of 15 are likely to go on to university, compared with 33 per cent of their wealthier peers.

Previous and current governments have attempted to improve education for poorer pupils - Labour through the academies programme and the Conservatives by encouraging the creation of “free schools”.

But the researchers argue that this has been counterproductive. “The marketisation of education works against the closing of the social-class gap, given the stronger purchasing power of the middle-classes and their ability to successfully play the game,” they said.

“It tends to be middle-class children within poorer schools who benefit most from school-based initiatives.”

Widespread preoccupation with exam results and league tables therefore means that poorer pupils quickly become disillusioned with education, the RSA academics say.

Policy-makers instead cite “low aspirations” as one of the barriers to working-class achievement: disadvantaged parents are failing to instil educational ambition in their offspring.

But, they added: “The projection of deficits onto working-class young people and their families has the potential to stigmatise these individuals.”

Meanwhile, few intervention initiatives value disadvantaged pupils’ own backgrounds. Instead, they try to turn working-class pupils into middle-class ones.

Initiatives also tend to concentrate on individual high-achievers, rather than on engaging all pupils. While this slightly increases the number of working-class applicants to elite universities, it does nothing to address the broader social divide.

The researchers concluded: “Focusing on engaging working-class young people with their education, as a necessary precursor to attainment, and valuing ... existing experience and expertise, are of fundamental importance in facilitating success.”

4% - 15-year-old pupils on free school meals who go on to university.