This summer's contentious shift in GCSE English grade boundaries was the "worst decision ever made by AQA", a senior figure from the exam board at the centre of the controversy has admitted, revealing it was done on statisticians' orders.
Emails from one of AQA's highest ranking assessors, seen by TES, also admit that the dramatic change in grade boundaries between January and June did "massive damage" and "instantly hit the most vulnerable" pupils.
The revelations were made in messages to a GCSE English moderator at AQA, who this week resigned in protest at the board's "morally repugnant" handling of the affair.
Stephen McKenzie, who worked for the board for 16 years before quitting, said AQA had reneged on guidance to schools about what a C grade should look like. He also said that claims of teachers over-marking controlled assessment were based on "paltry evidence" and that the moderation of the qualification was "chaotic".
The revelations are another blow to regulator Ofqual's position that the June grade boundaries were correct and set by examiners "using their best professional judgement, taking into account all of the evidence available to them".
Letters obtained by TES have already shown that Ofqual forced another exam board, Edexcel, to make significant last-minute changes to GCSE English grades that examiners had insisted were "fair" and backed by "compelling evidence".
There have been suggestions that Edexcel was out of line with other boards and attempting to award higher grades to attract more business. But the emails and Mr McKenzie's resignation letter reveal that assessors from AQA - the board with the biggest market share in GCSE English - were just as concerned as their Edexcel counterparts about the grading changes.
Brian Lightman, general secretary of the Association of School and College Leaders, said: "This is another example of the overwhelming evidence for regrading these exams as a matter of urgency in the interests of fairness."
In one message the senior assessor, who worked on GCSE English, writes to Mr McKenzie: "What caused the massive damage that you refer to was the statisticians' insistence that Paper 1 F (the lower tier English exam paper, grade C boundary) should go up by 10 (marks out of 80 between January and June).
"This instantly hit the most vulnerable part of our population and you know where it has got us."
Mr McKenzie's resignation letter claimed that the board's "mismanagement" of the affair was "particularly morally repugnant" because it hit lower- ability pupils.
"This qualification was directly marketed by AQA at students who would have had to work hardest to achieve a C or better," he added.
An AQA promotional brochure, seen by TES, said that the GCSE English qualification increases the "accessibility" for "foundation tier candidates". It pledged: "We will provide resources focusing on how to move your students from D to C grade . as well as student-friendly advice for reaching the vital C grade."
Mr McKenzie's resignation letter accused the board of "reneging on its own descriptions of a C" to schools, by shifting boundaries this summer.
The letter also described the AQA and Ofqual argument that teachers marked controlled assessment too generously as "disingenuous". Mr McKenzie, who checked such marking for AQA, noted that moderators would typically only look at 3 per cent of work at a school.
"To take a decision that scaled back the marks for tens of thousands of students based on such paltry evidence seems desperate," wrote Mr McKenzie, vice-principal at the Morley Academy, Leeds. He goes on to describe this year's moderation process as "poor, stressed and chaotic" and claims that a "significant" number of moderators may not have had experience of teaching the qualifications, as AQA had required.
In an email to Mr McKenzie, the senior assessor said they had "never known chaos like it". "And that's without the grading fiasco," they added. "The worst decision ever made by AQA."
AQA would not comment because of potential legal action over GCSE English. Ofqual said examiners had "acted properly" and that the evidence they used included statistics as well as candidates' scripts.
The wait continues .
Ofqual has failed to publish its correspondence with exam boards about this year's English GCSE grades, more than four weeks after it first pledged to do so.
On 28 August, Ofqual chief regulator Glenys Stacey told TES: "We are quite happy to put in the public domain all of the exchanges that we have with exam boards, with government, with anybody. We have nothing to hide here and we wish to be absolutely transparent."
But as TES went to press this week, the watchdog had still not published any of its exchanges with exam boards.