Mark Thomas lost his coveted place at Oxford University thanks to a mistake by A-level examiners. Instead of the A-grade he needed to secure his place at the university, he was astonished when he nervously opened his results envelope to discover that he had a B in geography. Gone, at one stroke of the examiner’s red pen, it seemed, were his Oxford dreams.

Like thousands of sixthformers since 1999, when he sat his A- levels, Thomas, now 25, was the victim of botched marking — serious mistakes that all too often change children’s futures.

Close on 11,000 GCSE grades were revised upwards last summer and more than 5,000 A-level grades. In some cases a missed grade, sometimes by just one or two marks, will cost a child a highflying career as a doctor or lawyer.

“It is outrageous,” says Thomas, who is now training to be a barrister. His school told him to accept the outcome but he decided to appeal to the exam board.

Six weeks after he had started a degree at Sheffield University, his second choice after Oxford, the board contacted Thomas. Examiners had made a massive error: after his geography papers were re-checked he was awarded an A. The mark in one of his six modules was increased by 10%, in another by 23%. “I believe that an error on that kind of scale is negligence,” he says now.

Although Thomas had to take an enforced gap year before he could start at Oxford on the basis of his changed A-level results, the board offered only £250 compensation.

It’s an all too familiar story. Kris Murali’s son, a straight-A student at GCSE, was surprised when his AS grade in chemistry slipped to a B. His school, Dr Challoner’s grammar in Amersham, queried the result. It promptly rose to an A.

Murali, a company director from Buckinghamshire, says: “My advice to parents is, if you have a doubt about a mark, challenge it. These are landmarks in a child’s life.”

James Burnett, a director of studies at the tutorial college Mander Portman Woodward (MPW) in London, also tells students to query suspicious results. Spectacular mistakes do happen, he confirms. “We had one student who got five marks out of 90 in a history paper. All his other papers were straight As. We sent it back for a re-mark and it went up by 50 points. Around 20% of the students whom we advise to appeal will see their grades go up.”

One such is 18-year-old Shaun Mohanaraj, a student at MPW who was celebrating last week after learning that the OCR exam board had decided to award his biology A-level papers one extra mark. That was all he needed to push his B grade up to an A. Now he’s anxiously waiting to find out whether his B in chemistry will also be upgraded on appeal.

“It will make a big difference: if I have two As and a B I can apply to study dentistry,” he explains. “With three Bs I would be looking at maybe engineering courses.”

But has the pendulum swung too far? The surge of errors by the five main exam boards in England and Wales has sparked a boom in appeals. Last year saw a record number being both lodged and granted. At GCSE level one in four were upheld; at A-level, successful appeals are running at one in 10.

The real unfairness now, say critics, is that many schools which use the system succeed in boosting pupils’ grades, while others never bother to challenge results.

At Eton college, where 500 results were queried last year and 300 revised upwards, head Tony Little says: “Any good school will review the marks its candidates receive to ensure they seem fair and consistent.”

So if your child sat A-level, GCSE or AS exams this summer, scrutinise their marks and be prepared to get your cheque book out (£35 for each re-mark). You have 17 more days until September 20 — the deadline for appealing. After all — your child’s future may be at stake.

IF YOU DON’T MAKE THE GRADE, THEN PAY THE PRICE

This sorry saga reveals the true extent of the crisis that is destroying public and professional confidence in the exam system. Mistakes in the grading of millions of scripts are inevitable, but not on this scale.

The boards have failed to recruit sufficient numbers of experienced examiners to do a decent job. Those they do have work under intense pressure and are paid peanuts. Arithmetical errors and administrative cock-ups combine to blight what may well be thousands of children’s lives. The exam boards have to improve their performance, and those that cannot should be shut down.

The number of appeals inevitably rises each year as confidence in the system plummets. It is clear, though, that some schools, driven by fear of league table humiliation, are encouraging parents to pay for appeals against exam board decisions as a matter of routine. This might be understandable but it is unacceptable.

Measures are needed to discourage those who at present rush to lodge a speculative appeal. If, for example, schools and parents knew that an unsuccessful appeal would see the cost double or triple then the decision to appeal might be taken more seriously.

Chris Woodhead