Nearly four in ten schools in England are planning to reduce staff numbers over the next 12 months as headteachers struggle to balance their books, according to a survey of senior leaders.
A joint survey by heads' union the NAHT and The TES has revealed that 37 per cent of schools are expecting to see their staff headcount fall.
One "conservative" analysis suggests that this will see the overall national figure for school staff drop by over 17,000.
Almost 1,500 heads and senior staff responded to the poll, which also showed that 40 per cent of schools were anticipating a slump in their budgets - 5 per cent of them said they are bracing themselves for a cut of more than 10 per cent.
But it is the fall in staff numbers - through a combination of redundancy and "natural wastage" - that has been met with most concern.
NAHT general secretary Russell Hobby said the figure for job losses was conservative, due to the number of smaller schools his union represents, and he warned that the cuts would be repeated for the next four years.
"The drop in the number of school staff may not seem that high, but we have to remember this is only in one year, and it is expected to get worse in following years," he said.
According to Brian Lightman, general secretary of the Association of School and College Leaders, the decline in staff will mean some schools will struggle to support the pupils who need it most.
"It is a very significant figure, and we have been warned that this is just the beginning," Mr Lightman said.
"People are planning for a contraction and the only way to do this is through a reduction in staff."
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