Kate Plumb, 21, from Berkhamsted, Hertfordshire, has finally been awarded the B grade she needed for her university course after her parents launched a three-year battle with the exam board.
The misgrading forced her to miss the last year of free higher education and left her parents facing a pound;1,000-a-year bill for tuition fees. Her case has also highlighted the difficulty in getting boards to reconsider decisions.
Kate's father, Chris Plumb, a civil servant, said: "The whole system conspires against an individual who tries to get an injustice corrected.
"The exam board tried to give us the brush-off many times. It makes you realise just how many people have probably suffered a similar injustice but have accepted what the board tells them or don't have the time or determination to persevere."
Kate, who would have graduated this summer, was forced to take a year off after the examiners of her 1997 drama A-level awarded her a C rather than the B grade she needed for a place on a drama degree course at Royal Holloway college, University of London.
The low grade was almost entirely due to an extremely low mark for one paper - a live drama performance.
Roal Holloway offered her a place on the same course starting the following year where she is now in her second year.
When her father queried the result with the exam board Edexcel, he was told that it could not be investigated because the evidence of Kate's performance was ephemeral.
He said: "I was infuriated by this as no other body would be able to run a system that wasn't auditable. You cannot have an examiner making judgments about someone if there is no way of checking what they have done. It made me determined to continue."
In its last case before it was replaced by the Examinations Appeals Board, the independent exam appeals panel, the IAASE, ruled that Edexcel had been unfair in the marking of Kate's live performance and had acted improperly in allowing the examiner's report to be destroyed before the Plumbs' case had been resolved.
The board had also misled the family by informing them that the case could not be reviewed, it ruled.
Following the appeal decision, the Plumbs have had Kate's tuition fees refunded.
Richard Dalziel, headteacher at Ashlyns School, Berkhamsted, where Kate was a pupil, said: "Kate's father is the real hero of this case. If he had not been so tenacious in pursuing this there is no way the exam board would have upgraded Kate's result."