Independent school pupils are up to five times more likely to achieve the highest marks at A-level than their state school counterparts, research obtained by The Sunday Telegraph has revealed.
The statistics, compiled by the largest exam board, show that if a "supergrade" were introduced to distinguish between candidates with A grades, the gap between state and private pupils would widen dramatically. In some subjects, such as physics and German, independent school pupils - who are already twice as likely as state pupils to obtain an A grade - would become five times more likely to gain the highest mark.
The research will embarrass the Government and reinforce the suspicion of critics that it has failed to introduce an A-plus grade because this would make it far more difficult to persuade universities to discriminate in favour of state pupils. Whitehall wants universities to discriminate and is offering financial incentives to those that do and threatening financial penalties against those that do not.
Dr Martin Stephen, the chairman of the Headmasters' and Headmistresses' Conference, which represents 240 leading independent schools, said: "These figures show that pupils at independent schools are performing extremely well. "Universities should take students on the basis of their academic achievement. Going on anything other than achievement brings in discrimination that is immoral and probably illegal."
Philip Evans, the headmaster of Bedford School and the chairman of the independent schools' university admissions committee, said last night the figures proved private pupils were being discriminated against and called for an A-level supergrade. "At all levels within the A grade, independent school candidates seem to be winning hands down. Introducing different levels within the A grade would be a simple solution and make it more discriminating at the top end. It could be done tomorrow."
The new research was compiled by the Assessment and Qualifications Alliance (AQA) from the results of A-level candidates in 2003, and sets out how pupils would have performed if an A-plus grade had been available. This would have required pupils to achieve at least 560 points out of 600, rather than the 480 needed at present for a standard grade A.
In geography, just over 18 per cent of comprehensive school pupils achieved grade A in 2003, compared to 41 per cent in the independent sector. If an A-plus grade had been awarded, however, the difference would have been far greater. Only 1.7 per cent of the grade A comprehensive pupils would have achieved the top level, compared with almost six per cent from the independent sector.
In Physics, the gap is even wider. The proportion of independent school pupils gaining the standard A grade in 2003 was more than double that in the state sector. However, while almost nine per cent of independent sector pupils gained enough marks for an A-plus, the corresponding figure for comprehensive pupils was only 1.6 per cent. This means that private pupils would have been more than five times as likely to earn the top grade in Physics than those in the state sector.
A spokesman for the AQA, which deals with 250,000 A-level entries each year, said: "The paper shows that at A-level, the independent sector does much better than the comprehensive sector in the proportion achieving grade A and if there was an A-plus they would do even better."
Leading universities want greater differentiation of A-level achievement because of the time and expense of whittling down candidates.
Follow me on Twitter: @IanYorston