The number of pupils achieving top grades in GCSE French and German has plummeted by up to 25 per cent over the past five years, prompting complaints from headteachers.
Exam boards are effectively making it harder for pupils to gain A-star to C grades because they have failed to take into account the effect of lower-ability teenagers dropping the subjects, heads have claimed.
A TES analysis of results shows that the number of pupils gaining an A- star in French fell from 25,046 in 2002 to 21,022 in 2007, a drop of 16 per cent. In German, the number has fallen by 25 per cent.
The boards said this was because far fewer candidates were taking French since it became voluntary in 2004. Candidate numbers fell from 338,468 in 2002 to 216,718 this summer, a 36 per cent drop.
Our analysis shows that although there has been a drop in A-stars, entries have fallen faster, meaning that the proportion awarded the top mark has actually grown steadily in recent years.
But some heads, particularly in the private sector, say that high- achieving pupils are being penalised. Although entries have fallen, few A- star pupils have dropped the subject, they believe.
They argue that a pupil who was the 25,000th best in Britain at French in 2002 would have got an A-star then, but only an A now.
The same trend was reflected in the number of C grades and above, which have also dropped.
The independent St Albans School in Hertfordshire has unearthed figures showing that grade boundaries for AQA French and German listening and reading tests have risen dramatically since 2003.
In German listening, 14 out of 45 marks were needed for a C grade in 2003. This year, the figure was 25. In French listening, 24 marks out of 45 achieved an A-star in 2003, compared with 33 this summer.
The school believes the exam board is making it harder for higher-grade pupils to do well for fear of an outcry if numbers gaining A-star stayed roughly the same while candidate numbers dropped.
This summer, of the school's 1,244 GCSE grades, only 16 were below a C. Thirteen of these were in French and German.
Andrew Grant, the headteacher, said: "The Government did its best to kill off languages when it made them voluntary. The awarding bodies are now doing their best to burn the corpse."
A report in May by Lord Dearing, the Government adviser, recommended a review of languages at GCSE level to address concerns that they are harder than other subjects.
An AQA spokesperson said: "The AQA has maintained the GCSE modern languages standard as constant during this period of change and decline in entry patterns."
The board's statistics showed it was not just the lower achievers who had dropped the subject, she said. Many candidates from the upper end of the ability range had also opted out of languages.