Schools entering pupils for GCSEs on multiple occasions are “doing real damage to education in this country”, exam boards warned this morning.

The boards stand to gain financially from practice, which has increased exponentially over the last three years, but today said it had reached such a high level that they felt compelled to speak out.

Mark Dawe, chief executive of the OCR board, said: “There is limited educational benefit in multiple entries. We all believe the accountability system is putting pressure on schools and teachers to follow this practice.”

Figures released by the boards today show nearly a quarter of students - 24 per cent - were entered for maths GCSE twice this academic year and that another 10 per cent were put in three times.

“There are two poor souls who actually took maths GCSE eight times this year,” said Andrew Hall, chief executive of the AQA board.

The figures were “starting to stretch credibility” if it was suggested that they represented a natural re-sit pattern, he said. “Those are seriously expensive costs for the economy and are actually doing damage to mathematical education in the UK,” he added.

This summer the Department for Education calculated that the cost of additional entries in GCSE English and maths was more than £11m in 2011, rising to £13m in 2012. The practice was costing hundreds of schools at least £6,000 a year.

Brian Lightman, general secretary of the Association of School and College Leaders, said league tables were “driving practice” and forcing schools to place an emphasis on pupils achieving grade Cs.

“With the high stakes system, the very rigorous way Ofsted is looking at these grades and the importance of having Cs for future career opportunities, schools are required to do everything they possibly can to get as many people through Cs and that is why we are seeing this move towards early entry, double entry, use of the IGCSE,” he said. “It is all understandable.”  

But Mr Hall said: “Mathematics for me is the biggest concern that comes out of all of this with that repeated multiple entry. I think that is doing real damage to education in this country.”

Today’s figures also reveal a 39 per cent rise in GCSE entries from students who were 15 or younger this year. They made up 806,141 entries, nearly 15 per cent of the total.

Mr Dawe said: “Early entry does not benefit the students - the results are far lower for those students at 15, in general, than at 16. These qualifications were designed for 16-year-olds.

“If there is a 10 per cent difference in pass-rate [between 15 and 16-year-olds] that is not good for the student. They should be left to learn for those two years and then take the exam. That is what we would encourage.”

Department for Education research shows that early entries in GCSE English climbed from 9,000 in 2005 to 174,000 in 2010.

In GCSE maths the practice climbed steadily between 2005 and 2009 from 24,000 to 59,000 and then shot up to 152,000 in 2010.

Exam board statistics released today suggest it has since increased even more dramatically this academic year with a total 565,833 GCSE maths entries for the November, January and March exam sessions.

Hr Hall said the tight regulation of the exams industry meant there was nothing the boards could do to stop the practice.

“We are being vocal about it because we are concerned about it,” he said. “People say well you get money from it, yes we do, but that’s why we want to draw it to people’s attention because we can’t turn entries away.”

Asked if he was defending schools’ tactics, Mr Lightman said: “I am not justifying it, I am understanding it, and I am saying it is the accountability system driving that sort of practice. You can understand why any school will do everything it possibly can.”

But Sir John Rowling, the former head who founded PiXL, a group of schools using tactics to improve GCSE performance highlighted by TES last year, mounted a strong defence.

“If you are trying to get an Olympic qualifying time, you would be in a foolish position if the athletics board said you’re only allowed to pass it in Sheffield on 27 June. But people don’t do that,” he told the Guardian. “Some of these kids, their performances are just a little bit erratic. Let us try to work the best way we can to level that out.”