The ethnically diverse specialist language school, in a deprived area of the capital, has seen a 47 point jump in the proportion of pupils getting five Cs or better at GCSE from 2000 to 2003, when it reached 79 per cent.
Haydn Evans, the head, said the extra cash that had come with specialist status - an initial pound;150,000 and an extra pound;130,000 each year since - had been crucial . "We have invested heavily in ICT and built a new independent learning centre," he said, "and employed more staff."
Three in four of the school's 1,100 pupils qualify for free meals. And although Sir John Cass is a Church of England school around nine out of 10 pupils are from ethnic minorities, with many of Bengali Muslim descent.
The school offers 10 languages at GCSE to reflect this ethnic mix, including Russian, Urdu, Turkish, Cantonese and Bengali. Four out of five pupils who took a language gained good GCSEs in the subject in 2003.
The last inspection report in 1999 said the school had done well in raising standards given its intake at 11.