The publication of the independent sector's own A-level performance tables was met with mudslinging as leading headteachers attacked colleagues who have boycotted the league.
Today's table, shows that students at independent schools received twice as many A-grades as their counterparts in the state sector this summer. Some 52.3 per cent of all entries from independent schools gained an A-grade pass, up from 50.7 per cent last year. The national average this year was 26.7 per cent. On the overall pass rate, the independent sector scored 99.4 per cent, compared with a national average of 97.5 per cent.
But around 70 leading schools – including Eton, Winchester, St Paul's and Perse School for Girls in Cambridge, one of the top performing girls' schools in the country – have refused to take part in their sector's exam league tables.
Cynthia Hall, headmistress of Wycombe Abbey school in Buckinghamshire, which topped the table, led a staunch defence of A-levels and insisted that the exam was still demanding.
Mrs Hall, whose school had a point score of 497 – the equivalent of at least four A-grade passes for every pupil – added: "A-levels are still an appropriate challenge."
However, she acknowledged that students today had "much more information about what is expected of them", adding: "There is much more transparent information from exam boards, you can get sample work information about how examiners are marking."
Richard Cairns, the headmaster of Brighton College, launched an attack on those heads in the independent sector who were ditching A-levels for alternatives such as the new Pre-U, which is along the lines of traditional A-levels but without coursework, and the International Baccalaureate. "A-levels have a currency in the workplace that other exams simply don't have," he said.
"It is the role of responsible independent schools to work to improve our national exam system, not abandon it for alternatives that either fail to insist upon a proper understanding of our own nation's literary or historical hinterland as the IB does, or, like the Pre-U, hark back to a golden age that never was."
He added: "A-levels are imperfect but so too is the IB and the Pre-U. If independent heads really cared about our nation's education, they would not abandon the A-level for flawed and faddish alternatives. Working well, the A-level is a world-beater."
Mr Cairns said of those boycotting the publication: "It is patronising to suggest that parents are confused by league tables and therefore they should not exist. Fee-paying parents have the right to know what results our pupils achieve. Good schools should have nothing to hide."
Those boycotting the tables say they do not give an accurate picture of what they offer, particularly now that sixth-formers are offered more alternatives to A-levels. Perse School for Girls, which is boycotting the tables for the first time this year, claimed the results were a "flawed beauty parade".
The improved grades are being seized on by leaders in the independent sector to mount a defence against threats such as the possible loss of charitable status for those not deemed to be fulfilling a "public good".
David Lyscom, the chief executive of the Independent Schools Council, said: "These results, in particular the increasing levels of achievement in crucial subjects such as maths, science and languages, further underline the wider benefits generated by independent schools for the public and society, and notably the huge positive contribution they make to the UK's future economic success."
Separately, independent schools that offer their pupils the IB are publishing their own results. King's College, Wimbledon, tops the table with a point score of 625 – well above that of any school just offering A-levels. In the results table for state schools, which was published last week, Hockerill Anglo-European College in Bishop's Stortford, Hertfordshire, which offers its pupils the IB, came top in the non- selective section.
Exams: A testing subject for schools
*Controversy over the independent school league tables has pitted headteachers against each other. Richard Cairns, the head of Brighton College, is the most vocal critic of those who have decided not to submit their school's results for publication. He believes strongly that parents are entitled to the information.
Martin Stephen, the high master of St Paul's boys' school in London, is one of the fiercest critics of the tables, believing they do not give parents a clue about what schools are offering.
The controversy over the separate Government league tables – to which independent schools do have to submit their results – is just as fierce. These tables do not include the results from exams such as the IGCSE (International GCSE), which many independent heads favour because it is based on the traditional O-level (without coursework).
As a result, Winchester, one of the leading fee-paying schools in the country but which does not offer the GCSE, comes bottom.