Image caption Subjects like maths and modern languages may suffer under planned changes to A-levels, say heads

The take-up of 'tough' subjects like maths at A-level in England may drop if AS-levels are removed as a 'stepping stone', head teachers have warned.

In an open letter to the Education Secretary Michael Gove, head teachers' leaders say planned changes to A-levels risk narrowing the curriculum.

In a separate move, Mr Gove has written to the regulator Ofqual setting out a timetable for the changes.

Ministers say the new 'linear' exams will boost students' subject knowledge.

The plans mean that from 2015 all modular units will be scrapped, with pupils taking A-level exams at the end of two-year courses.

The AS-level exam will remain. Currently it is taken after a year and counts towards a full A-level. It will instead become a stand-alone qualification with exams after one or two years in the sixth form.

'Stepping-stones'

Mr Gove believes that A-levels in their current form are not rigorous enough and do not help students develop deep understanding of their subjects.

But the open letter, signed by the leaders of four associations representing head teachers from both state and private schools, urges Mr Gove "in the strongest possible terms" to retain the current AS-level, as a "stepping-stone" to full A-levels.

The letter warns that "unless universities include the proposed 'stand-alone' AS-levels in their offers, and there is no reason to believe that they will, their take-up in schools and colleges is likely to diminish".

The heads' leaders argue that many pupils currently take AS-levels in contrasting subjects alongside their main A-level subjects, adding breadth and flexibility to their learning and encouraging the take-up of important, but tough subjects such as maths and modern languages.

If the value of AS-levels is diminished to students, the uptake of these subjects at A-level may drop, they argue.

Breadth and challenge will be reduced and the main losers could well be further maths, languages and other subjects which are viewed as more difficult Brian Lightman, Association of School and College Leaders

Brian Lightman, of the Association of School and College Leaders (ASCL), whose annual conference opens on Friday, suggested that some schools might decide simply to do three A-levels and ignore AS-levels altogether.

"Breadth and challenge will be reduced and the main losers could well be further maths, languages and other subjects which are viewed as more difficult."

The letter also argues that AS-levels play a vital role in encouraging "less confident students" to continue with their studies.

"Without validation at the 'stepping-stone' point, less confident students are likely to be discouraged from embarking on A-levels in the first place," it says.

Christopher Ray, of the Headmasters' and Headmistresses' Conference, which represents independent school leaders, told BBC News the new system could potentially harm "students who only when they get their AS-level results in Year 12 realise how bright they are, who are perhaps in an underperforming school or college and who suddenly have the self-confidence to aim for the stars".

"Without that self confidence they won't go for it," he said.

However, in his letter to Ofqual, Mr Gove suggests that although AS-levels will be entirely decoupled from A-levels "to become a stand-alone qualification that is also linear" their course content should be compatible: "Any subject content changes made to the corresponding A-level should be reflected in the design of the AS."

Assessment 'burden'

Mr Lightman welcomed this suggestion - as having the same course content would mean that A-levels and AS-levels in the same subject could be taught in the same class, boosting the uptake of AS-levels.

However he warned that there was a danger that some schools might decide to enter pupils for four of the new AS-level exams in Year 12, followed by three full A-levels in Year 13.

"This could add enormously to the burden of assessment and there is no sound educational argument for this."

A spokesman for the Department for Education said: "We are reforming the A-level system to make it more rigorous, with academics at our best universities advising on their content.

"We fully expect schools and colleges to continue to ensure that pupils take the A-levels that are right for them, especially in the key academic subjects which keep their options open."

Head teachers are likely to challenge Mr Gove on the issue when he addresses the ASCL conference later on Friday.

The letter was also signed by Martin Doel of the Association of Colleges and Russell Hobby of the National Association of Head teachers.