An examination board found evidence of malpractice at an academy school highly praised by Prime Minister David Cameron, according to documents released on Friday.
OCR said that as a result of adjudged instances of maladministration and malpractice found in the administration of GCSE Science coursework at Kingsdale Foundation School in Southwark, south London, it lost confidence in the validity and reliability of the marks submitted by the school.
The school was described as "brilliant" by Cameron in May 2011, but allegations about practices there were made by whistleblowers in July that year.
OCR said that with regard to the production of coursework, candidates confirmed that the practice was for a first draft to be written and marked by the teachers. Candidates were then given another opportunity to complete it.
Its report said: "These statements reflect some of the allegations made by one of the whistle-blowers and evidence to support the claim was found as multiple copies of the coursework with earlier drafts and improved second drafts existed. This practice does constitute malpractice."
OCR decided to discard all the coursework marks and give candidates an assessed grade for the coursework units based on examined units. Candidates received a full grade for GCSE Science at the usual time, the report says.
Specific demands of the centre were made in a letter in October 2011 from the chief executive of exam boards' umbrella body the Joint Council for Qualifications (JCQ) to the school's chair of governors, the report says.
These related to the strengthening of the role of the Examinations Officer, the conduct of examinations in line with JCQ rules and the correct delivery and assessment of internally assessed units.
It was also deemed necessary to place a JCQ inspector full time in the school during all 2012 exam periods, but no further problems were uncovered.
The report was released by qualifications regulator Ofqual as it believed it was in the public interest to do so.
OCR said the investigating team did not find any evidence to support allegations relating to exams being taken at the wrong time or in the wrong place. It was also confident that invigilation was in line with regulations. There was also no evidence that science teachers were providing candidates with additional support during their examinations.
Another exam board, AQA, said evidence was found of irregularities in the management of coursework and the submission of marks to the board in relation to GCSE English and GCSE English literature.
Another board, WJEC, said the handwriting of three candidates varied across scripts in different subjects. It was determined that "unauthorised emergency scribes" had been used, "even in cases where the candidate had been capable of writing", and no details of the scribes used were kept.
Ofqual said the reports had not been agreed by the school, where there was no one immediately available to comment.
The school's headteacher, Steve Morrison, later invited Ofqual to release all other reports over the same period "as we believe there is nothing exceptional about the Kingsdale case other than the orchestrated provocation of a media storm".
He said in a statement: "We recognise the published reports are internal communications between the examination bodies and Ofqual and have a specific and limited remit, perspective and objective.
"We have expressed our concerns to both Ofqual and the examination bodies over what we consider to be misleading and/or inaccurate statements contained within them particularly with respect to the report from OCR.
"We intend to make further representations as we do not believe the public interest is served by ambiguous or erroneous reporting. We thank Ofqual for noting that the school does not agree with all aspects of the reports.
"The school is not averse to such reports being published subject to accuracy and the requirement to protect individual confidentiality.
"We would welcome a move to greater transparency in such cases and invite Ofqual to release all other reports over the same period as we believe there is nothing exceptional about the Kingsdale case other than the orchestrated provocation of a media storm.
"We are confident that outcomes compare favourably to many other inquiries over the same period in spite of the extended forensic examination of the school. In this respect, the most significant outcome of the investigation is the fact any historic deficiencies or irregularities identified by the school or the examination bodies related almost exclusively to the work and responsibilities of purported 'whistleblowers'.
"The governing body wishes to confirm that the outcomes of investigations have produced no evidence at all of institutional or systemic malpractice or maladministration at the school. There can be no doubt that in this respect the school has been fully exonerated.
"No sanction or warning has been issued against any individual connected to the school who was the subject of an allegation by a third party.
"One warning (which is the lowest form of sanction) was issued against an individual who was formerly associated with the school based on evidence supplied by the school.
"Parents, students and the public can have confidence in the integrity of past, current and future examination grades awarded at the school.
"The school now considers this matter closed.
"The Governing Body has been provided with compelling evidence that there was a coordinated campaign against the school and specific individuals within it.
"The Governing Body would like to express its gratitude to our wonderful students, staff, parents and the overwhelming number of well-wishers whose faith in the excellence of the school has been fully justified."