More than 27,000 pupils sat a two-year-old history paper for their International Baccalaureate (IB) diploma last week.

The error was discovered after pupils left the examination, saying that they had seen the paper before. The board confirmed in a note of apology to schools that a “grave mistake” had been made.

In December Tony Blair said 100 state schools would each receive £26,000 to cover the costs of introducing the IB. Forty-four independent schools and 51 state schools and colleges offer it. In the past two years 18 state and 13 independent schools have adopted it as an alternative to A levels.

George Pook, the IB assessment director, said that the mix-up was caused by “human error” after a leftover history paper from 2005 that no candidate had sat was earmarked for this year’s exams. But the paper that was sent out instead had been taken that year by several thousand students worldwide.

“The people involved are very upset about it and would like to apologise to all the pupils involved,” Mr Pook said.

A history teacher at a London school said that he was astonished by the error. “It’s absurd, I’ve never heard anything like it,” he said. “We took the IB because of all the stories of incompetence regarding the A level. What I’m not happy about are the ramifications. I fear students could lose out.” But Mr Pook insisted that students would not be penalised and that sitting a past paper would have provided “no significant advantage” for most pupils. Results will be analysed in an attempt to ensure fairness. “We want to provide the grades that give a fair reflection of ability and not prior knowledge of the questions. Our expectation is that this will only affect a very small number,” Mr Pook said.

The paper, which was taken last Wednesday, posed 30 questions about six topics, of which candidates had to answer two, each in 45 minutes. About 28,000 candidates took the paper worldwide. The IB charges about £4,500 to each school and £300 for each student taking the exams.

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