New evidence of the pressure on schools to get students across the C/D borderline at GCSE was revealed by Ofqual today. 

For the first time, the exams regulator released figures for appeals against individual grades, which showed that 38 per cent of all appeals at GCSE involved students who had been given a D. 

Secondary schools have a floor target of 40 per cent of students achieving five A* to C grades, including English and maths. A failure to meet this benchmark could result in a change of leadership, Ofsted inspectors being called in and even the possibility of being converted into an academy. 

Overall, almost 330,000 appeals were launched against GCSE and A-level exam grades this summer – 13 per cent more than in the previous year, when a controversy over the English GCSE grading led to a legal challenge from headteachers and others.

This year 54,350 grades were changed, one in six GCSE appeals resulted in a new grade and one in five A-levels.

At A-level, where there is no C/D threshold, it was a B grade that was most likely to be challenged, accounting for 33 per cent of appeals.

The 329,906 appeals this year compares to 291,111 last year, when 46,226 grades were changed.

Glenys Stacey, chief regulator of Ofqual, admitted that "external pressures", such as the government's accountability measures at the C/D borderline, were having an impact on appeals.

“Today’s statistics show a rise in the number of appeals and the number of grades being changed as a result.

“But it is important to see these statistics in context: while appeals have increased by 9 percentage points this year, they still represent only 2.3 per cent of all exams marked by examiners, with less than a fifth of those appeals resulting in a grade change."

Ms Stacey said while the upward trend of grade changes did "concern" her agency, it represented just 0.6 per cent of all exams taken. 

“We are evaluating the reasons behind the increase in appeals and grade changes, and for the first time this year we show the number of enquiries at each grade. For GCSEs we found that the focus is at the C/D borderline. This shows us that external pressures, such as accountability measures, are influencing decisions to appeal,“ she added.

Pressure on schools has been particularly intense as attempts to clampdown on grade inflation continue. This year the proportion of students getting A* - C grades dropped from 69.4 per cent to 68.1 per cent. 

Sue Kirkham, curriculum and assessment specialist at the Association of School and College Leaders, said that there was also increased pressure on students who now have to continue to study GCSE maths and English after 16 until they get a C grade.

She said: "The number of appeals show that people are rather lacking confidence in the way grades are awarded at the moment. It also shows the very, very high stakes nature of the current accountability system where everything rides on whether you get a C or a D."

Last year an alliance of unions, councils, schools and pupils attempted to overturn English GCSE exam grades through a judicial review.

The legal challenge last year failed, but the Commons education select committee looked into the situation and stated that "confidence in the exam system has been shaken". 

In 2012 the grade boundaries were changed during the year so those sitting the exam in January had more generous boundaries than the majority who sat it in June, but the judge found it was the structure of the qualification, not the actions of Ofqual, that caused the unfairness.