The students are now lacking confidence over their future and they have had to do resits when they need not have done

Gareth Jones

The revelation involving the AQA exam board comes after a series of blunders involving another board, Edexcel.

All 22 students at the south Wales school had their papers remarked and their grades increased after the results were given out last August.

One girl's mark moved from an E to an A in the regrading.

The Manchester-based examination board AQA admitted its mistake and wrote to Mr Jones to saying the marking was "unsatisfactory" and apologised.

But Mr Jones said the regradings did not come until the last day of last term, and four students had since dropped history at A-level.

"It's been very distressing for the students," Mr Jones told BBC News Online on Wednesday.

'One-off situation'

"The students are now lacking confidence over their future and they have had to do resits when they need not have done."

Mr Jones said the mistake appeared to be a "one-off situation", but it had caused a lot of distress and worry for both students and staff.

"When the results first came in last August the staff noticed the grades were way out of line with what they would have expected the students to achieve," said Mr Jones.

"So a batch was sent in for remarking and when they came back altered, all 22 pupils had the paper remarked."

"One girl came back with her grade changed from an E grade to an A."

The student involved, Sian Warrilow, has since dropped the subject.

Her father, who is head of Carntown Primary School, Pontyrpridd, said she might have contined with history if the paper had been marked correctly.

The Assessment and Qualifications Alliance (AQA) came into existence in April 2000 following the merger of the Associated Examining Board and the Northern Examinations and Assessment Board.

It is the largest of the three English unitary awarding bodies.