Figures released in the annual report of the Specialist Schools and Academies Trust show that the extra resources given to specialist schools have failed to raise attainment in modern languages above the national average.
In German, just 60 per cent of pupils at specialist language colleges got an A* to C grade, compared to 67 per cent in other schools. In French, the difference was 58 per cent compared to 59 per cent.
Only in Spanish did the specialist colleges outperform other secondaries, with 62 per cent of pupils getting an A* to C grade compared to 60 per cent in other mainstream schools.
The report says the results can partly be explained by the fact that more pupils take those subjects at specialist language colleges than in other schools. Although pupils are not forced to take language GCSEs, specialist colleges will often encourage more to do so.
David Crossley, director of achievement at the SSAT, said: "Specialism leads to greater take-up of those subjects and generally improved performance. But if you double the amount of pupils, you are drilling further down into the ability range."
John Bangs, head of education at the National Union of Teachers, said: "It is an indictment that the motivated minority in non-specialist schools do better at languages. It shows language learning is not properly embedded in primary and secondary education."
The report, which analyses school results in 2006, also contains the first review of the value added results of the 141 selective specialist schools.
It shows that, as in non-selective schools, girls significantly outperform boys, with the gap only narrowing for the top achievers. Overall, selective schools achieved an average of 57 per cent of pupils getting five A* and A grades at GCSE last year.
Results varied considerably among different types of specialist schools, with city technology colleges topping the list of those exceeding their predicted results. Engineering, sport and combined colleges were at the bottom, all failing to reach their predicted performance.
"It is surprising to find such a wide range of differences in added value between specialist schools types. This matter clearly needs to be subject to further review," the report said.
Elsewhere, the report debunks the suggestion that specialist schools have improved their results and league table positions by offering vocational equivalents to traditional GCSEs.
Figures show that vocational qualifications made up at least 10 per cent of exam entries in only 5 per cent of specialist schools. In non-specialist schools more than 10 per cent hit the same mark.
"This contests the observation that specialist schools' performance, improvement and added value are due to excessive use of these newer routes.
In fact, the opposite is the case," it says.
Sir Cyril Taylor, chairman of the SSAT, congratulated the schools on their results. Overall, 60 per cent of specialist schools achieved five GCSEs grade A* to C compared to 48 per cent of non-specialist schools.