Headteachers are drawing up plans to cut the number of A-level courses they offer students and increase class sizes in other areas to deal with spending cutbacks.
A-level funding has not been ring-fenced by the Government like other areas of the education budget, and schools have been warned they could face budget shortfalls of up to 20 per cent.
As a consequence they are examining the option of reducing the range of choices available to sixth-formers and cutting subjects with a low take-up. They are also looking at increasing class sizes or reducing lesson time, with pupils being taught online instead of by a teacher.
Most at risk of cutbacks are modern languages such as French, German and Spanish, as well as Latin. The drastic options are a result of cuts to school sixth-form provision over the next three years.
The dilemma arises because sixth-form funding does not come through local authority funding, but from a Government quango called the Young People's Learning Agency. It has been told to reduce the level of financial support by 20 per cent over the next three years.
Brian Lightman, general secretary of the Association of School and College Leaders (ASCL), warned that school sixth-form funding had been the worst hit part of the education service. As a result, the A-level – which has long been considered the "gold standard" of the examination system – will bear the brunt of the cuts, he said, adding that this was "really worrying".
Mr Lightman was speaking after secondary school headteachers in Sheffield wrote to parents in the city warning them of the dilemma they faced. "Subjects where low numbers of students choose them may not run in all institutions," they wrote. "Class sizes may well have to rise in some subjects to ensure financially viable groups."
The Sheffield heads say they face cuts of between £120,000 and £457,000 per school – up to 14 teachers' salaries. They claim that the range of subjects offered by their schools might have to be reduced, so arrangements with neighbouring schools would have to be sought.
"We are planning for budget cuts arising from inflation, increased pension and national insurance contributions," the teachers added. "Sixth-form funding cuts will be in addition to these... This is a serious set of circumstances: we have never been subjected to cuts of this magnitude."
"This is the case across the country," Mr Lightman said: "The amount available for post-16 education is the area that has taken the hardest hit. In schools, post-16 students are going to face a difficult three years."
He said that those schools opting to become one of the Government's academies could be cushioned in the first year – because they would receive an extra grant to compensate for lost services from the local authority. However, even they would be hit in the ensuing years, Mr Lightman added. He said the ASCL had sought to bring the funding plight to the attention of ministers.
The Sheffield headteachers have urged parents to write to their local MPs – one of whom is the Deputy Prime Minister Nick Clegg – and Michael Gove, the Education Secretary, to protest. One of the reasons school sixth-forms are suffering is as a result of a government pledge to put them and further education colleges on an equal footing for funding. In the past, schools have been funded more generously than colleges.
However, Mr Lightman said it would have been better to avoid a time of financial squeeze to do this – so that college funding could have been increased to the level of school sixth-forms rather than school funding being reduced.
A spokeswoman for the Department for Education said: "We are moving towards a fairer and more transparent funding system for further education. For years, school sixth-forms have been funded at on average £280 more per pupil than further education colleges – for a medium- sized college this would be the difference of around £500,000.
"In the current economic climate it does not make sense for this inflated funding to continue so we are moving to a level playing field. We have put in place transitional funding arrangements to help school sixth-forms adapt."
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