Language teaching has declined markedly in some schools
The teaching of modern languages is being "damaged" by efforts to make their study optional at GCSE level, a survey suggests.
At one school, the proportion of 14 year olds dropping subjects like French and German altogether rose from 40% to 90% in just a year, according to Cilt, the National Centre for Languages, which advises ministers.
It is calling for "coherent support" from head teachers and local authorities to ensure languages do not decline further.
The comments come as the government is planning to remove them from the core national curriculum for 14 to 16 year olds from September next year.
Many schools have already made languages optional in anticipation of this.
Of those which have done so, 51% reported that more than half of pupils had dropped out at 14.
A Cilt spokesman said: "Clearly, damage is being done to languages departments in this situation.
"Schools should be warned against introducing ill-considered options systems which will weaken their ability to offer high-quality teaching in Key Stage 3 [ages 11 to 14] and have a detrimental effect on the motivation of pupils at all levels."
The survey, of 146 schools, found take-up rates for German and French had declined from 1996 to 2002. Spanish, however, enjoyed a rise in popularity.
Sometimes, streaming systems meant less able pupils were guided into non-language options.
However, even more gifted pupils often chose other subjects instead.
Cilt also reiterated previous findings by the University Council of Modern Languages (UCML) that three-quarters of higher education institutions had cut certain languages.
This, it said, had happened "solely in response to local institutional demands, with no discussion of local or regional needs".
The changes at school level, had led to fewer working-class children going on to study languages at degree level.
Only 12% of entrants were from lower social-class backgrounds, compared with 15% for all subjects.
Hilary Footitt, chairman of the UCML, said: "It is extraordinary that at a time when the government has developed its first National Languages Strategy, calling for more graduates in more languages, no one seems to care that actions by individual vice-chancellors could be de facto sabotaging the policy."