A school previously rated as good has been told to improve its teaching.
King Solomon High School in Forest Road, Barkingside, was also criticised by Ofsted for a high level of fixed-term exclusions.
A report published last week found the school’s self assessment of performance was “too generous”.
Inspectors said the number of pupils making progress in English was well below the national average, while the number of students making expected progress in maths was in decline.
General progress among pupils was found not to be quick enough and too few knew how to improve their work.
The report said it was too soon to evaluate the impact of Headteacher Jo Shuter, who was appointed in October 2013.
However, it added: “The new headteacher has had a very positive impact on the school. She is developing strong and capable leaders at both senior and subject levels who have the capacity to develop the school further.
“They know that the school requires improvement, but leaders are skilled and able to take on this challenge.”
The Jewish secondary school was rated good by Ofsted inspectors in 2011.
Jo Shuter was named the country's best headteacher in 2007 for her work at the Quintin Kynaston Academy in St John's Wood, but stepped down after being disciplined by governors over her expenses.