Hundreds of GCSE, AS and A-level results have been re-graded after errors were made in exam marking.
The OCR exam board said it apologised "unreservedly" for the mistakes, which were made by examiners, and insisted that action had been taken.
In total, 98 GCSE, 285 AS-level and 50 A-level results, were revised upwards after being re-marked.
The errors came to light in the autumn and were due to "human and process errors by a minority of examiners", the board said.
Schools and colleges with affected students have been told, OCR said, and they will pass on the results to their pupils.
It is not known if any of the affected A-level results had an impact on students' university places. Students are often given places on degree courses based on their exam grades.
OCR chief executive Mark Dawe said: "On behalf of OCR, I apologise unreservedly to the students, parents and teachers affected. I would like to reassure students taking their exams with OCR this summer that due to the rigorous new measures we now have in place, these issues cannot occur again.
"We have conducted extensive investigations into what went wrong. With the help of our most senior examiners, we reviewed all the relevant papers from last summer's exams and increased marks on a tiny percentage of papers as a result.
"Although these changes represent less than 0.03% of the results we issued, we are continually improving our processes to drive down the incidence of marking mistakes."
OCR said in a statement that the re-grades were necessary to correct mistakes identified by the board in the marking of four A-level history and English units and the use of an "incorrect code" on a limited number of papers.
" These were the result of human and process error by a minority of examiners during the transition to online marking," the board said, adding that "t he examiners involved will no longer work for OCR".
"New and enhanced marker monitoring is one of the improvements OCR has introduced for the summer 2014 exams and additional analysis will be undertaken at the end of the marking process.
"OCR is reviewing and strengthening its processes for standardising examiners and clearing them to mark, and remains vigilant to the concerns of schools on this key issue."