One in four maths lessons in secondary schools is taught by teachers who have never been trained in the subject.
Figures reveal that at least 750,000 youngsters aged between 11 and 16 are taught maths by untrained staff. Even a rise in the numbers of would-be maths teachers attending training courses is failing to dent the problem, according to Government maths experts.
Many newly trained teachers only last two or three years in the profession before moving on to more lucrative careers in the City or elsewhere in the private sector.
"The behaviour of pupils is often cited as a reason for leaving," said a member of the national literacy and numeracy strategy team.
"Frankly, they can earn more money with much less hassle outside the classroom. Maths is seen as a hard subject. The kids behave badly in maths."
Ministers have been warned the situation is likely to get worse, with many serving maths teachers reaching retirement age over the next few years. The figures show that only 75 per cent of lessons are taken by trained staff. Other teachers - such as psychology, science or even (in some cases) languages staff - stand in, often on a long-term basis.
"There are highly qualified maths teachers in schools who won't be very good teachers and, equally, teachers with very little maths background doing a very good job," said the team member. Overall, though, lessons by non-specialists were less effectively delivered - with the prospect that they could turn youngsters off the subject.
Maths experts said that the shortage of recruits created a catch-22 situation. Fewer pupils were inspired to study maths as a subject up to A-level with the result that it became even harder to recruit trained staff to teach the subject.
One glimmer of hope is that some of those who quit to join the private sector are now beginning to return to the classroom later.
However, a maths expert added: "I don't think the situation is getting any better. We're recruiting more into initial teacher training courses - but we're still not getting the numbers we need into the profession.
Yesterday's comments follow the publication of this year's annual report by Ofsted, the education standards watchdog, which revealed half the country's secondary schools (51 per cent) were failing to provide a good education. One of the reasons cited was recruitment problems - in subjects such as maths and science.
Ministers are forging ahead with plans to introduce a new compulsory functional skills tests in the basics - maths, English and IT - at GCSE level, to be taken by youngsters for the first time in 2011.
Under it, all youngsters will have to sit maths test or prepare a maths portfolio. If they fail, they will be ineligible to receive a C grade or above pass in their GCSE maths exam.
* The Government's exams watchdog yesterday effectively vetoed the use of the International GCSE in state schools. The qualification is more akin to the old O-level, with a reduction in coursework, and is increasingly used by fee-paying schools.
The Qualifications and Curriculum Authority said in a report that it did not meet the standards demanded by the national curriculum. It said the exam failed to offer enough material for low achieving candidates in French, and did not include a maths paper where students were forbidden to use a calculator.Reuse content