A state-funded orthodox Jewish girls' school in north London has been criticised after it was discovered that dozens of pupils had their GCSE exams censored, with questions about evolution deliberately blacked out of science papers.

The OCR examinations board found that 52 papers in two GCSE science exams sat by pupils at Yesodey Hatorah Senior girls' school in Hackney this summer had questions on evolution obscured, making them impossible to be answered.

"Ensuring the integrity of the exam system is of paramount importance to OCR and we will always take all the steps necessary to protect it," a spokesman for OCR said.

The exam board said it was holding discussions with the school to ensure that the episode was not repeated, as well as raising its concerns with the Department for Education and schools watchdog Ofsted, as well as the Joint Council for Qualifications of exam boards.

"We have tried to respect the religious and cultural sensitivities of this community while protecting the integrity of our exams. That said, we do not consider obscuring aspects of question papers to be good exam practice.

"We are also in the process of agreeing safeguards with the school to ensure good exam practice in the context of today's pluralistic society. Ofqual are also fully aware of our investigation and its outcome," OCR said.

Yesodey Hatorah is a voluntary-aided all-girls school, meaning it is fully funded by the government but retains full power over its own admissions procedure. According to the school's prospectus it gives priority to admitting "Charedi Jewish girls who meet the Charedi criteria as prescribed by the rabbinate of the Union of Orthodox Hebrew Congregations."

Charedi Jews are often described as strictly Orthodox Jews, with Stamford Hill home to Europe's largest community of Orthodox Judaism.

The school's 2012 GCSE results were excellent overall, putting it in the top 20% of state schools. In GCSE science, 95% of its pupils gained a C grade or above, well above the national average of 75%.

The school was last inspected by Ofsted in 2006, and rated as outstanding. It had an interim inspection in 2010.

An Ofsted spokesperson said: "All schools should provide children with a good education. If Ofsted believed any school was deliberately preventing children from receiving a broad and balanced curriculum, this would be taken very seriously.

"As part of our risk-based approach to inspection Ofsted inspects schools rated outstanding less regularly. This school was rated outstanding in 2006 and then had an interim assessment in 2010 which found that its performance had been sustained. If Ofsted becomes aware of any information that proves otherwise, or if any other legitimate concern is raised about the school, this could trigger an inspection in line with our risk assessment policy."

According to the school's prospectus, prospective applicants are told: "Parents are expected to co-operate fully in insulating the children from undesirable external influences and fashion trends that conflict with Charedi Jewish values."

The prospectus also notes: "Charedi homes do not have TV or other inappropriate media. Parents ensure that their children do not have access to the Internet or any other media which do not meet the stringent moral criteria of the Charedi community."

The exam censorship came to light after complaints by the National Secular Society, after comments by Rabbi Avraham Pinter, the principal of Yesodey Hatorah, to the Jewish Chronicle, in which he said "sometimes Charedi schools, if they find anything in the paper which could be offensive to parents, advise children to avoid that question".

Stephen Evans, the National Secular Society's campaigns manager, said: "Faith schools such as Yesodey Hatorah not only impede social cohesion by segregating children along religions and ethnic lines, they also fail to prepare pupils for life outside of a religious community and deny young people the opportunity to reach their full potential."

The school could not be reached for comment.