One in four schools thinks it will offer a short course in modern languages next year but an alarming 80 per cent of those fear it will mean fewer pupils doing a full GCSE course.
This means the Government's new requirement that all pupils take a foreign language up to 16 may backfire. Those - often the less able - who currently drop a foreign language at 14 will now take one, although many will only do a short course equal to half a GCSE. But some of those who now take a full GCSE are likely to opt for a short course instead.
The TESCILT survey suggests that department heads are losing the battle with curriculum planners, who find short courses in modern languages a convenient way of freeing time for other subjects.
Out of 858 schools in England who responded on this question, just over half (53.6 per cent) plan to offer a full course to all pupils. A further quarter will offer a full course to some pupils and a short one to others. Only a handful - five schools - plan to offer a short course to all pupils. The rest - 15 per cent - did not know.
Most short courses seem likely to be spread over two years. Only a few schools said they were planning to offer a one-year "fat" course, although many had not yet decided.
Two hundred and twenty-two schools are planning to offer short courses; 181 thought their introduction would mean fewer pupils would take a full GCSE in a first foreign language and nearly one in four thought it would lead fewer pupils to take a GCSE in a second foreign language.
The survey suggests that nearly one in eight pupils do not study a foreign language after the age of 14.
Kathy Wicksteed, who chairs the policy committee of the Association for Language Learning, described the predicted fall in the take-up of full courses as "pretty worrying". She feared this would exacerbate the inequality between middle-class successful schools and inner-city ones that were already struggling with languages.
But a School Curriculum and Assessment Authority spokeswoman said it was hard to see why pupils who now took a full GCSE course when there was no compulsion on them to do so should stop because of the introduction of short courses. "Nobody can know at this stage. Time will tell," she said.