Teachers at a high-flying East London academy have claimed they witnessed coursework and examinations being marked falsely.
The tutors allege there was a “climate of intimidation and fear” at Green Spring Academy Shoreditch, where “dishonesty was the main ingredient”.
Head teacher Mark Keary was suspended last month over exam-fixing claims.
Green Spring Education Trust said it had acted robustly in dealing with the allegations.
Mr Keary, who was reportedly paid £220,000 per year, was suspended in February along with a number of other staff members.
An investigation into alleged misconduct in relation to some examinations had found “irregularities”.
The Department for Education (DfE) said exam malpractice had been identified and disciplinary action was being taken.
Mr Keary has not responded to approaches for comment.
GCSE results had gone from being among the worst in the country to making the academy one of the top-performing schools nationally.
In its latest results it recorded an 83% A-C pupil pass rate for GCSE English and maths.
Mr Keary took over the then Bethnal Green Technology College in June 2006 and oversaw its transformation into an academy at the start of 2012.
BBC London has heard from six former teachers who spoke of a culture of intimidation where some felt they had no choice but to cheat or leave.
Jahangir Alam left the school in 2012. He said: “It became like an exam-production factory.
“Everything was geared toward the exam and it really didn’t matter how you got the result.
“On a few occasions I have seen malpractice with coursework, meaning inflated coursework marks.”
John McKelvey, who retired after many years at the school, alleged there was a “climate of intimidation and fear”.
He said: “People would come into work one morning and, presumably, they were asked to leave and escorted from the premises.
“This happened to a large number of people, at least 10 that I know personally. This was very upsetting. People were watching their backs.”
He added: “I would say it would be extremely difficult to get those kind of [GCSE grade] percentages from the student intake as I remember it; very difficult indeed.”
A spokesman for the DfE said: “There is no place for cheating in our schools, and while exam malpractice is extremely rare, it is right that any allegations are thoroughly investigated.
“Following an investigation at Green Spring Academy in Tower Hamlets, exam malpractice has been identified, resulting in disciplinary action being taken.
“The regional schools commissioner is working closely with the academy trust to ensure students face as little disruption as possible during this time, and we continue to monitor the situation closely.”
In a statement, Green Springs Academy said: “The independent investigation commissioned by the trust board has now concluded and appropriate action is being taken which cannot be discussed for reasons of confidentiality.
“Working with key authorities, including the DfE, the trust board has acted robustly and with integrity in dealing with the allegations made.”
The school made headlines in 2015 when three pupils, Kadiza Sultana, Amira Abase and Shamima Begum, aged 15 and 16 at the time, left the UK during February half term for Syria.
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