By Katherine Sellgren BBC News Online at the NAHT conference in Torquay

Head teachers are warning that sixth formers are facing an exam overload.

The National Association of Head Teachers, meeting for its annual conference in Torquay, has heard claims that schools are becoming "exam factories".

There are worries that the AS-level usually taken in the first year of sixth form, plus the full A-level in the second year, has turned the sixth form into a two-year "cramming session".

Head teachers want A-levels and AS-levels to be re-scheduled so that students can have more time to study, rather than simply cram for exams.

This system is turning schools into exam factories

David Hart, National Association of Head Teachers

These concerns over exam overload have been echoed by Barry Sheerman, chairman of the education select committee.

"There is too much of an exam culture in our schools," he said. But he rejected calls for the scrapping of AS-levels, saying that it was a case of re-assessing the balance.

Head teachers say that the scheduling of exams also reduces the amount of time for studying.

They want AS-levels to be scheduled later in the summer term, after the full A-level exams, to allow more time for teachers and students to prepare.

Now the exam season is starting earlier than ever - this year on 13 May - cutting valuable lesson time, the NAHT warns.

"An exam system which gives 16 year olds only two terms in which to study for AS qualifications is absolutely ridiculous," said NAHT general secretary, David Hart.

"This system is turning schools into exam factories," he said.

The Liberal Democrats education spokesperson, David Rendel, said that too many exams were squeezing out other activities such as drama and the arts.

"Extra-curricular activities, such as school plays and community service, which are all part of the school learning experience, are abandoned as students are forced to focus on exams early in the first year of sixth form"

Cost of exams

The NAHT, which on Wednesday published a survey suggesting many schools were facing budget deficits, also raises concerns about the cost of so many exams.

Gareth Matthewson, head of Whitchurch High School in Cardiff, said his exam budget had risen from �80,000 to �120,000.

"And when you add in the costs of administration, the extra burdens on the exam officer and so on, it's actually �200,000 - now that's quite a strain on the budget," said Mr Matthewson.

Mr Matthewson said youngsters were being over-assessed.

"I have a Norwegian student in our school and she can't believe how much pupils in England and Wales are tested.

"In Norway they seem to have a much better system of continuous assessment and teacher assessment."

Delegates at the conference are also to set to debate the issue of teacher workload.

NAHT members could take industrial action if the government fails to fund a programme to reduce workload by the end of the autumn term.