Many schools have not taught languages courses, including French, German and Spanish, to children over 14 for two years.
It follows Government guidelines in 2004 that relaxed rules making it compulsory to study a foreign language for GCSE.
Critics warned it could damage Britain's "international competitiveness" by depriving students of essential language skills.
Nick Gibb, the Conservative schools spokesman, obtained the figures by asking a written Parliamentary question to the Department for Education and Skills.
He found 25 schools in England did not teach a single GCSE language course in 2006.
He said: "It will have a profound effect on the ability of British-educated children to secure jobs with employers in the global market."
A spokesman at Campion High School, Liverpool, said: "Boys in particular are choosing subjects that are easier to do than French would be."
In March, Education Secretary Alan Johnson pledged to shake up languages teaching by 2010. He said children as young as five should learn Polish, Afghan and even Somali.Reuse content