The country's worst-performing schools could be closed just five months after they are failed by Ofsted under tough new government guidelines.
The drastic action will be taken only in the most extreme cases. But it more than halves the time schools in special measures would have to show progress.
The guidelines, published last week and to be confirmed in the education Bill, say: "We cannot allow schools to remain in special measures for an extended period of time if little or no progress is being made."
John Dunford, general secretary of the Association of School and College Leaders - who opposed the 12-month deadline originally announced by ministers - said the shorter limit was even more unreasonable.
"This suggests a degree of impatience on the part of the Secretary of State which is severely at odds with what we know about school improvement," he said.
The guidance says: "An exceptionally severe series of findings at the first Ofsted monitoring could be sufficient for the Secretary of State to issue a notice that the case has become urgent."
An urgent notice is likely to trigger closure by councils, according to the guidance.
"The strong presumption at this point will be that the school should be replaced unless the local authority is able to make a very convincing case why an alternative solution that has not yet been implemented would result in better outcomes for pupils," it says.
Ofsted figures show that 244 schools were in special measures at the end of last year and that 159 had been so for longer than five months.