England's largest exam board has admitted that one of its most popular GCSEs has become easier.
AQA made the extraordinary concession about its GCSE science exam after reluctantly agreeing to a request from England's new qualifications regulator to lower the mark needed to achieve a grade C.
AQA believes that in doing so - which it did only "under protest" - it has been forced to follow other boards in making the exam easier than its predecessors.
However, rivals say the new science GCSEs are as difficult as they ever were. The revelations, which relate to controversial new GCSE science exams taken by more than half a million pupils, are the first time a board has publicly questioned the maintenance of standards for one of its exams.
They came after fraught discussions between the boards and Ofqual, the new exams regulator, which intervened to force AQA's hand on the eve of the results' publication in August.
The TES can disclose that rival board Edexcel awarded C grades in a paper for one of its new science courses to pupils scoring only 20 per cent.
In early August, England's three boards asked Ofqual to adjudicate after discussions between them failed to reach agreement on setting comparable grade boundaries for science GCSE.
On August 7, only two weeks before the results were due to be published, Ofqual wrote to AQA asking it to reduce the grade boundary for the crucial grade C below what the board had calculated was necessary to maintain standards.
This, Ofqual said, was to "bring it into line" with grading decisions at other boards. Mike Cresswell, AQA's director general, replied that it would do so only "on balance and under protest".
He wrote: "AQA is extremely reluctant to adopt a standard for GCSE which is less comparable with the past than it needs to be.
"However, AQA has a clear duty to the young people who took its GCSE science exam this year to ensure it does not suffer in comparison with those who took the examinations of other awarding bodies."
Dr Cresswell also said Ofqual had decided to make the recommendation to AQA "rather than requesting the other awarding bodies to adopt standards more clearly in keeping with those of the past".
Ofqual wrote back that all the exam boards believed their grade boundaries maintained standards with the past, and that its intervention would ensure this was the case across all boards. It is carrying out a review of the grading decisions, which will conclude next year.
Speaking to The TES this week, Dr Cresswell would not reveal what grade boundary the board would have preferred to have set but confirmed that the board stood by the letter.
He said: "I'm absolutely certain that standards between 2007 and 2008 could have been maintained more effectively. We would have preferred a solution that promoted standards that were a little more consistent with those of 2007."
Some 55 per cent of AQA's candidates gained a grade C this year in the main science exam, with 66 per cent doing so in additional science, compared with 52 per cent last year in the predecessor exam, double science.
The new science GCSEs, which have introduced media-friendly topics, such as genetic engineering and global warming, have drawn criticism for reducing the factual knowledge required, some dubbing them "science for the pub".
Professor Alan Smithers, of Buckingham University, said: "Ofqual's duty is to maintain standards. It does not seem sensible to try to do this by accepting the lowest common denominator on offer from the three awarding bodies."
Isabel Nisbet, Ofqual's acting chief executive, said: "We were trying, in quite a tight time window, to make a decision that was fairest to learners. It was not ideal that we had this choice to make."
The regulator is compiling a report on the standards-setting process for GCSE science, to be published in the new year.
Leading article, page 36.