Teachers have expressed outrage that the mark scheme for the coursework element of an A-level exam was changed after students had submitted their work.
One school has claimed that many of its 50 students lost a grade in their coursework because they were not notified of last-minute changes to the way psychology A-level was marked by the Oxford, Cambridge and RSA board.
The problems, which the board says did not affect students' final grades, appear to be a direct result of last year's regrading crisis.
Julian Pinches, head of psychology at King James school, Knaresborough, north Yorkshire, has written to OCR detailing ways in which the mark scheme changed this year so that his students lost the chance to score high grades.
For one section of the coursework, the new scheme assigns marks to students under four headings. Under "issuesassumptions", it says students have to refer to at least two areas of psychology. But under the old scheme there is no mention of this.
Under "presentation and communication", the new scheme says that, for the highest scores, book references used by students must be noted in the text.
But the old scheme merely says students get the top marks for "full references", meaning, said Mr Pinches, that most had just listed sources at the end of the text.
Finally, under "evidence", the new scheme says that to score highest, students have to show "detailed and apposite psychological evidence". The old scheme just says that evidence should demonstrate understanding and the relevance to the source.
Mr Pinches said students could lose 15 marks out of 40 by keeping to the requirements of the old mark scheme, rather than the new. "They've changed the goalposts. It's outrageous," he said.
The school is also appealing against what it claims is poor marking by the exam board.
Jane McGee, a psychology teacher from Kingsley College, Redditch, Worcestershire, said: "The mark scheme was changed, and no one was aware that it had changed."
A further education college told The TES of its concerns after most of its 80 students ended up with Es and Us for coursework.
Problems with OCR psychology coursework triggered last year's regrading controversy, as schools complained that A-grade students had been given Us for the coursework module.
OCR said that as a result, it had been ordered to change the mark scheme this year, to increase the number of marks covering grades A to U. Schools had been notified that there would be changes in April, but were not told what the changes actually were until July.
This, however, had not affected individual student grades because examiners were still looking for the same qualities in candidates.
Bene't Steinberg, OCR's head of public affairs, said: "Teachers are supposed to teach psychology. They are not supposed to teach to a particular mark scheme."