Children in areas where the teacher shortage is severe could have their school hours cut, according to John Dunford, general secretary of the Secondary Heads Association.
Latest figures show the Government's pound;5,000 "golden hellos" are failing to tackle the teacher-recruitment crisis in maths, science and modern languages.
Compared to this time last year, enrolments in teacher training in some subjects has plummeted, Mr Dunford told the SHA's annual conference in Harrogate last weekend. In maths, the figure is down by nearly a quarter, chemistry has a 22 per cent shortfall and modern language enrolments are 7 to 71 per cent down.
Mr Dunford said: "Now we have a position where the only secondary subject showing an increase in recruitment to initial teacher training this year is PE. This represents the strongest possible warning to the Government of the crisis in teacher recruitment.
"And if it will be difficult for secondary schools as a whole to recruit the brightest and the best, how much more difficult will it be for those schools which already struggle to attract any applicants - the very schools which need the most talented teachers.
"With the number of teachers leaving the profession, we are facing long-term melt-down."
Urgent measures were needed to change the public image of the teaching profession and improve pay and conditions, he said.
Mr Dunford added: "The change will not come about through the continued denigration of the work of schools and teachers."
But according to senior public servant Sir Michael Bichard, who is the
permanent secretary at the Department for Education and Employment, the teacher recruitment crisis has been
He said: "Recruitment is not at the crisis levels some people are suggesting."
While the pound;5,000 "golden hellos" were not a permanent solution to teacher shortages, they had produced an effect, Sir Michael added.