An investigation has been launched into the use of a new GCSE grading system, after results fell in three of the most popular subjects.
The Qualifications and Curriculum Authority is talking to all three boards about results in maths, French and German. Together, the subjects received more than 1.1 million entries this summer.
The proportion of pupils achieving grade C or better fell in maths from 51.3 to 50.2 per cent, in French from 53.6 to 51.2 per cent, and in German from 58.2 to 55.4 per cent this year.
The new scheme, adopted across several GCSE subjects for the first time this year, converts marks in individual papers to scores on a uniform mark scale, which are then added up to determine grades. Last year's outcry surrounding the grading of some students' A-levels followed the introduction of a new uniform mark scale for that exam.
The move comes as more teachers contacted The TES to claim that borderline C-grade pupils in French and German had been penalised by AQA, the largest board.
As The TES revealed in October, some teachers claim that students entered for the foundation tier in AQA French unfairly missed out on a C grade because of the way the new system works.
Phil Wood, modern languages adviser for Lancashire, said he had written to all of the authority's 88 secondaries, asking whether they had concerns about modern languages results.
More than 30 wrote back to say that grades were below expectations, with some reporting big disparities.
The problem itself is complex, but Mr Wood confirmed what other schools have told The TES: that foundation-level candidates, aiming to score a grade C, had found it harder to do so this year in the oral exam.
In addition, the board has told schools that, unlike last year, pupils had to achieve a C grade in all four papers of the exam in order to achieve a C overall.
This would appear to make the standard tougher this year than last, unless individual papers have been made easier.
Mr Wood said: "There are a number of schools which are very unhappy about what has happened this year.
"Many pupils, who they thought would have achieved a C last year, have not done so.
"The board has always been very supportive to our schools, it's just this one occasion where there seems something amiss."
Teachers claim that not only have individual C grade students missed out, but that they themselves are coming under pressure from headteachers and that some schools will drop languages next year as a result.
At Sandhurst school, in Berkshire, 18 per cent of pupils taking French and German achieved a C or better in speaking tests this year. In each of the past three years, the figure was more than 40 per cent.
Shirley Vandersluis, head of modern languages, said the marking scheme effectively stopped pupils entered for the foundation tier from scoring top marks in speaking tests. A member of AQA's advisory committee for modern foreign languages said the committee was concerned about the "depression" of results this year and had asked the board to carry out research on the reasons.
A QCA spokesman said: "As part of our routine monitoring we felt it was appropriate to evaluate the operation of the (uniform mark scale) conversion process to ensure that it worked effectively.
"Initial findings are that the system worked well. QCA and the awarding bodies are now looking in more detail at the system to determine whether any fine tuning is needed for the summer 2004 examinations."
George Turnbull, AQA head of public affairs, said that the board had looked into the issue after receiving some complaints from schools, but this had confirmed that "the results were as they should have been".