Education campaigners have welcomed a school's decision to scrap a disputed bilingual teaching scheme.
Some 59 languages are spoken at the school
Turkish pupils at the north London secondary school were being taught GCSE science in their native tongue.
But the new head of White Hart Lane school in Tottenham said pupils must focus on learning English.
Nick Seaton, of the Campaign for Real Education, said: "I fully support this move back to all English lessons and would think it is very overdue."
"If youngsters are going to come and live in Britain then they need to have a good grasp of the English language," he said.
"Teaching them in their own language is really not practical or helpful, especially when in this school there are so many different languages spoken."
More than 70% of pupils there have English as a second language and 59 different languages, from Amharic to Ukrainian, are spoken.
About 400 of the school's 1,200 pupils speak Turkish, and bilingual lessons were introduced in 2001 for those taking GCSE science.
But results for this group and for other students remained stubbornly low, with only 23% getting a grade C or higher at GCSE.
There were also plans to extend the scheme to Somali children.
Head teacher Joan McVittie said that "these children will live and work in London and therefore what we need to be doing is improving their competence in English".
The initiative was praised at the time by Education Minister Stephen Twigg as "very much the kind of good practice we want to promote".
But a spokesman for the department for education said: "English language fluency is a priority for all pupils."