Headteachers were in revolt last night as new figures showed the number of schools failing inspections has almost doubled since the beginning of the school year in September.
The numbers written off by inspectors as "inadequate" have shot up from just four per cent to 7.5 per cent in the wake of a tougher new inspection regime introduced by Ofsted, the education standards watchdog.
In addition, the percentage rated as "outstanding" has slumped from 19 per cent to 9.2 per cent.
Ofsted said last night that more than 2,000 schools had been inspected under the new regime, meaning that the figures show 150 have failed compared with around 80 in previous years. The number rated outstanding would similarly have fallen from 380 to 184.
The figures have infuriated headteachers – many of who are worried they will be threatened with the loss of their jobs if schools are declared inadequate. They warn that it is now virtually impossible for schools in deprived areas to be ranked outstanding.
Under the new procedures, schools are marked down if they have low exam results – even if they are serving deprived neighbourhoods. John Dunford, general secretary of the Association of School and College Leaders, said: "Lowish raw results (in exams) will automatically pull down the judgement on achievement and the domino effect will pull down the judgement on the whole school."
Speaking at his association's annual conference in London, he added: "Ofsted said it was raising the bar with the latest inspection framework but we didn't realise they were going to double the height that schools had to jump."
He said the figures, from an analysis of inspections by the Times Educational Supplement, were "very worrying".
In his speech to the conference on Sunday, he will add: "Raw results represent young people's life chances, so of course they are important but the inspection grade should recognise the context – that it is much harder for some schools and colleges to get good raw results."
A breakdown of the figures revealed that the rise in primary schools being declared inadequate was higher than in secondary schools – increasing from three to 7.3 per cent. Among outstanding schools, the percentage of secondary schools had fallen from 22 per cent to 9.5 per cent.
Schools Secretary Ed Balls said: "They (Ofsted) did raise the bar. They also have skewed their inspections away from strong schools."
He insisted, though, that it was still possible for a school in a deprived area with lower attainment to be ranked outstanding.Reuse content