Heads have raised fears that Ofqual will usher in a system that limits the number of pupils achieving top grades, after the exams regulator announced an overhaul of GCSE English marking.
The watchdog revealed last week that exams or coursework completed next January will be marked but not given a grade until the June exams are also marked. Ofqual is making the change as it attempts to avoid a repeat of this summer's fiasco, in which GCSE English grade boundaries were raised in the middle of the academic year. The shift led to thousands of pupils gaining lower than expected grades, heads claim.
But the decision has triggered concern that it will enable Ofqual to adjust grade boundaries to the proportion of students achieving certain test scores, known as "norm referencing". GCSEs are supposed to be "criterion referenced", rewarding pupils regardless of how their peers perform.
Not giving pupils grades after their January exams will also make it more difficult for teachers to judge pupil progress, teachers have warned.
"This change means Ofqual can adjust the standards for what is needed for a grade B or a grade C," said Brian Lightman, general secretary of the Association of School and College Leaders. "There should be an objective standard that is known to everyone, as GCSEs are criterion-referenced exams. It should not matter when the exams are taken. This change is a type of norm referencing and that is absolutely not what GCSEs were designed for."
The changes to GCSE English were set out in Ofqual's report into the grading crisis, published earlier this month, which claims that teachers were guilty of "significant" overmarking of pupils' coursework because they used inflated January grades as a guide.
Confirming the changes, Ofqual issued a statement last week saying that the report "identified a number of risks which could still affect 2013 students". "Therefore this change is being made to protect those students as much as possible, and to protect the security and standards of the qualifications," it added.
But the overhaul has been interpreted by some teachers as a way for Ofqual to give itself greater power to set grade boundaries "behind closed doors" at a time when the government is intensifying pressure to curb "grade inflation".
Nick Hackett, vice-principal at Ansford Academy in Somerset, said it would allow "wiggle room to massage the figures". "This can't go on indefinitely," he added. "The real casualties are the students, but also the schools who try to get some momentum going only for the goalposts to be moved once again."
John Tomsett, head of Huntington School in York, questioned why the watchdog felt it needed to make the changes. "Every utterance that has come from them is that they have done nothing wrong and that they were right to change the grade boundaries. If they were so right, why make these changes now?" he said.
An Ofqual spokeswoman said: "There is no expectation that the grade boundary marks for the January and June written papers will be the same - they will be set separately on the different papers. Therefore students will be judged on the paper they sit.
"Exam boards will set the grade boundaries based on all the available evidence, as they always have done. It is Ofqual's job to monitor this and make sure that standards are maintained year-on-year and across exam boards. We do not use a 'norm referencing' approach," the spokeswoman added.
Ofqual's announcement comes just weeks before a judicial review of its refusal to regrade pupils affected by the fiasco.
The problem of maintaining standards when using modular exams was first highlighted by Ofqual three years before this summer's grading fiasco.
As TES revealed in September, the exams regulator raised concerns about pupils being able to "bank" grades early.
Grading of individual modules could mean that when it comes to the overall grade the "outcome is automatic", the former chief regulator of Ofqual, Isabel Nisbet, said in October 2009. "The machine goes ping and out pops the candidate's results. There is no discretion."