Frances Wood, head of the Chinese department at the British Library and author of dozens of books, loves history. And until last summer, so did her son Ed.

Described by teachers at a top private school as “the best historian we have had in 15 years”, the 19-year-old was predicted to hit straight-A grades in his four A-level subjects. Cambridge had already offered him a place to study for a history degree.

But when his exam results arrived last August, his parents were flabbergasted. Nestling among the three A grades for drama, English and Latin was an E grade for one of his six history papers, scuppering Ed’s chances of going to Corpus Christi College.

Ed and his parents were as shocked as his Westminster school teachers. Since several pupils had performed worse than expected on that particular paper – on Charlemagne – the school sent their papers be remarked by the Oxford, Cambridge and RSA (OCR) exam board.

“Ed’s confidence was really rocked,” said Wood last week. “Many of the pupils in the class did surprisingly badly on that paper. My understanding is that, on a remark, many of their marks went up – and the grades of the entire class were then reviewed by the board. But Ed’s marks didn’t initially increase enough to give him an overall A-grade A-level. ”

Dissatisfied with the result of Ed’s remark, the school took the case to an independent appeal. Then, earlier this year, the mark was pushed up again, giving him the A-grade in history that he had deserved all along. It had taken six months – and by then the Cambridge place had been withdrawn.

“It is so appalling to be remarked on a paper and go all the way from an E to an A or a B. How can the board hold its head up?” asked Wood. “The fact that so many pupils were upgraded shows that the school did not teach the paper badly; the marking was wrong.”

Her son, Wood says, has taken the blow better than his parents. “My husband minds even more than I do,” she said . “He wanted desperately for our son to go to Cambridge. I minded less because I went to Cambridge and I just remember there being upper-class twits all over the place.”

Instead, Ed went to Leeds (his second choice) “where,” said Wood, “he scores consistent firsts in his essays”. She feels that bad examiners should be named, shamed and sacked. “I feel so angry with the board.”

This story is far from unique. Thousands of children every August open their results envelopes to uncover astonishing GCSE and A-level grades. Twenty-three thousand GCSE and A-level grades had to be changed last year. Sadly, some blunders are never corrected, in some cases blighting teenagers’ prospects.

The unfairness of the system is even more pronounced in comprehensive schools. At fee-paying and grammar schools, teachers are well-briefed and usually appeal any suspect results immediately. But at comprehensives, mistakes often go unchallenged – partly because of the cost and time involved in querying grades (a remark of just one paper costs about £30, which many families cannot afford).

And if the exam board insists on sticking to its guns, there’s little that can be done. Appeals can be taken to the independent Exam Appeals Board only on a technicality, so few cases get that far. Legal challenges are rare and difficult to pursue.

Tom Hill tried to sue the OCR exam board for £100,000 in 2002 when he was awarded an unexpected unclassified grade in his history A-level after studying at Marlborough college in Wiltshire. “We had it remarked by three A-level official markers from another school,” said Tom’s father, Graham. If their new marks had been accepted by the exam board, Tom would have secured his place at Oxford. Instead, he “lost his [university] place and felt let down by the very institutions he had trusted”.

Not that Tom has been held back. He went on to take a double-first in history and war studies at King’s College London, graduated top of his class, won a distinction for his MA and is now studying for a doctorate.

The government has promised to overhaul the flawed exam-marking system, in which the exam boards are both judge and jury – and last week published a report on the steps it plans to take. But details of how the new system will work remain veiled in confusion and there is widespread suspicion that any changes will do little to disturb the status quo.

Meanwhile, back in London, Frances Wood is still waiting for an apology. She may have a long wait. “We don’t deal with parents or students, but with schools,” said a spokeswoman for the exam board. “Obviously, it is disappointing when we pick up a mistake like this, but such mistakes are rare.” Judging by the Sunday Times postbag – not that rare.

How we can sort out this exam appeals mess

Last year, the number of mistakes made by the GCSE and A-level exam boards rose by 14%. Ken Boston, the chief executive of the Qualifications and Curriculum Authority, the exams watchdog, reacted dismissively. “It is a tiny proportion,” he said, “of the number of exams taken.”

But Boston’s claim that very few scripts are actually regraded is disingenuous. A survey that the QCA commissioned showed that one in three teachers do not trust the exam system. Why should they, when up until the very last stage of the appeals procedures, the exam boards are judge and jury in the investigations?

When Hannah Longman wrote to ask me to investigate why one module of her history A-level had been awarded an E – when all the others had scored top marks – I asked two teachers at a top independent school to look at her script. They said that her work was worth at least a B grade. The exam board did not, of course, change her mark.

If we want a fairer exam system, we need an appeals process that is independent of the exam boards at all stages.

How, though, can the number of mistakes be cut down? The number of exams students are entered for must be reduced – nobody should study more than eight GCSEs. This would ease pressure to find examiners.

At the moment, too, many teachers do not want to mark exam scripts because the pay is so bad. So remuneration must be addressed. And finally, markers should be freed from the constraints of prescriptive mark schemes designed to eliminate professional judgment.

Chris Woodhead

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