Some 250 students sitting tests last year have been told they will receive higher marks – with some papers being inflated by two grades – following a major miscalculation by examiners.
In some cases, it is feared that errors may have affected pupils’ university applications.
The OCR exam board said mistakes occurred while examiners were “transcribing and totalling” marks in a warehouse last summer.
In a statement, the organisation said four examiners had been sacked and another 78 had been given official warnings following a nine month investigation into the incident.
Earlier this year, it emerged that a whistleblower who personally contacted a series of schools to inform them about the blunder had been suspended.
Mark Dawe, chief executive of OCR, one of Britain’s biggest exam boards, apologised for the “unacceptable” error and insisted a new clerical checking regime had been introduced to root out further mistakes.
But the latest disclosure will heap further pressure on examiners following a series of high-profile blunders in recent years.
Last summer, at least 10 mistakes were found in A-level and GCSE papers set by exam boards across Britain – affecting hundreds of thousands of pupils.
In December, boards faced further criticism when an investigation by the Telegraph found senior examiners advising teachers about the exact wording that pupils should use and which questions they could expect.
Mr Dawe said: “Mistakes were made by examiners in the transcribing and totalling of marks. These are unacceptable and OCR apologises to students, schools and parents that our high standards for quality and integrity were not met by some individuals during routine processes.
“I have taken a number of corrective actions to address these matters including terminating four examiners’ contracts, placing another 78 on notice to improve and instituting a new clerical checking regime.”
It emerged that scores on more than 250 test script were incorrectly added up by examiners marking traditional pen and paper scripts. Some 180 schools were affected.
As a result, grades were improved in 15 A-level papers, 28 AS-levels, 37 GCSEs and 34 “short course” GCSEs.
Of those, five candidates saw their qualification improved by two grades. This included a GCSE in religious studies that was inflated from a B to an A* and an A-level in physical education which improved from C to A.
It is not known how seriously the errors effected individual pupils, although any major miscalculation with A-level results could have undermined students’ attempts to get into certain universities.
Many units taken as part of two-year A-level and GCSE courses – where students are due to receive final grades this summer – have also been affected. Some 81 A-levels and 56 GCSEs are to be marked up and taken into account when final grades are awarded in August, OCR said.