Schools complain that candidates who display originality are being let down by inflexible marking schemes and poorly qualified examiners.

In one case a state grammar school was so angry when one of its pupils was given a D grade that it asked Cambridge, where he had an offer of a place, to re-mark the paper. The university judged that it should have been at least two grades higher and awarded him a place.

In another case a teacher at an independent school and a former examiner complained when a pupil was marked down to a D after presenting a carefully argued case that the Vietnam war could be partly explained by decolonisation. The exam board claimed the pupil, who was holding an offer from Oxford that he lost as a result, gave “too much context”. When he answered a similar question in a similar way in a re-take, he got an A grade.

The cases underline a growing dissatisfaction among schools that “tick-box” marking schemes are failing to give credit to exceptional work. The number of A-level papers where schools have sought re-marks has risen by 20% in two years.

In 2003, schools requested re-marks on 36,000 A-level papers because they judged the grades “unfairly low”. By 2005 it had risen to 43,500, with 5,273 resulting in higher grades. At GCSE, re-marks have increased by more than half to 55,400, of which 10,848 were upgraded. Eton College returned 500 A-level papers last year. Exam boards gave higher marks to 299, 113 of them enough to raise grades.

John Bald, an education consultant, said: “Boards are trying to get a grip on the expansion in numbers of pupils getting top grades by using rigid mark systems that do not take account of exceptional intellectual ability.”

Adam Bracey, then a pupil at Maidstone grammar in Kent, was awarded a D in one paper, dropping him from an overall A to B in history. He needed three As to take up his offer from Cambridge. “I was devastated,” said Bracey, “some of my friends had got into university without the grades they had been asked for, but Cambridge was insistent.”

The Edexcel board refused to accept the D grade had been mismarked. Neil Turrell, his headmaster, sent the script to Cambridge after two staff concluded the grade was too low. Bracey, 20, got the place after a history don at Homerton College, where he is studying, agreed it was worth a higher grade.

Garth Collard, a former history teacher who had been part of the team inspecting Maidstone grammar for Ofsted, also read Bracey’s returned script. “I was shocked at the quality of the marking,” he said. “The mark scheme was very mechanistic . . . there was no recognition this was a high calibre answer.”

Other schools are concerned boards are not employing enough high-quality markers. This year Portsmouth grammar had a number of AS-level papers in English upgraded, including one from D to A. It comes as more than 100 independent schools are planning to ditch A-levels in favour a tougher qualification that places less emphasis on “mechanistic” course work and unlimited resits of exams.

Sophie Garrett, 18, who took A-levels this summer at Tormead, an independent girls’ school in Guildford, Surrey, had her music coursework regraded from unclassified to B. Her mother Valerie said: “The original mark meant she failed to get an A. It didn’t matter for her place at Surrey University, but she had put hours and hours into it.”

Exam boards said their marking schemes did not hold back brighter students. Edexcel said: “Candidates will always receive a fair mark for their work. All examiners must meet certain criteria. Markers are trained and tested to ensure they understand and follow the mark scheme.”

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