Pupils hoping for better A-level grades on appeal are much more likely to be successful with one exam board than another
Schools are nearly twice as likely to get A-level grades changed by one exam board than another.
An international assessment consultant has examined re-marking figures from the past five years and concluded that they show major, consistent differences in a supposedly standardised system.
George Bethell, director of Anglia Assessment, looked at the Qualifications and Curriculum Authority's (QCA) annual reports on GCSE and A-level enquiries and appeals for all three English boards. He found the most striking differences were between AQA and OCR.
Last summer, AQA changed one in seven A-level grades on appeal, while OCR changed just one in 13.
A similar pattern is seen at GCSE, where appeals to AQA had a one-in-four chance of a grade change, while those appealing to OCR had a one-in-six chance.
Mr Bethell said: "You don't have to be a bookmaker to see that the odds offered by the two boards are very different. This cannot be a random effect."
He said that either AQA's initial marking contained more errors than OCR, or OCR was more reluctant to change grades.
Last week, The TES reported AQA saying "some errors of judgement or process" in grading were inevitable. It warned that boards could face an annual bill of up to pound;1 million for wrong grades if a new exam regulator made them compensate candidates for mistakes.
But AQA denied its high proportion of grade changes was a result of its markers being error-prone.
A spokeswoman said: "The recently published QCA figures show that AQA has proportionately fewer enquiries about results than the other English awarding bodies.
"When dealing with a re-mark request, our policy is to apply every mark change, however small."
A spokesman for OCR said: "We believe that the relatively low number of grades that are changed demonstrates the professionalism of our examiners and our commitment to ensuring that all learners get the grade their work deserves."
The TES reported a leaked memo from OCR last year, encouraging examiners not to change marks without "very strong grounds".
Figures for Edexcel, the third main English exam board, showed that at A-level it usually finished between the other two in terms of the proportion of appeals that led to grade changes.
At GCSE, Edexcel made the second largest number of changes in 2003, 2004 and 2007; and the most in 2005 and 2006.
A QCA spokesperson said: "The number of changes following a remark is low, and the review process has ensured that each student has now received the correct mark. However, it is clear that awarding bodies must do further work to improve their quality assurance procedures, and we will continue to monitor their processes."
(*QCA or Edexcel comment to come).