Twenty struggling Midland schools were given a year's countdown to improve or face closure by the Government yesterday.
Under new get-tough plans announced by Education Secretary Ruth Kelly, schools put in special measures for failing will only get 12 months to turn themselves around.
If they do not, they will face a "more radical option," such as federating with a successful school, closure and re-opening as a city academy or under new management.
Ms Kelly said the proposals were aimed at preventing schools falling short for the "entire length of a pupil's secondary education".
But teachers and local education authority chiefs accused her of heaping pressure on heads and not giving schools enough time to work through changes.
Union leaders also accused the Government of having a "secret agenda" to create more privately sponsored city academies. Speaking at the Local Government Association Conference in London, Ms Kelly said: "We cannot ask children in our weakest schools to be patient while their school gets a second, third or fourth chance to improve.
"So being in special measures for more than a year without showing adequate progress must become a thing of the past."
The 12-month deadline halves the time recommended to get a school back on track by Ofsted.
Four primary schools and one secondary would face closure in Birmingham under the proposals which will be pushed forward in a White Paper later this year.
Les Lawrence (Con Northfield), the city's Cabinet Member for Education, criticised the clampdown.
"We have always had a view in Birmingham that two years is the appropriate length of time to turn a school around, because you need to change the management of the school if it has moved into a declining position. What the Secretary of State talks about a year, it isn't a year because there are only 192 days in the school year.""
Kevin McCabe, who took over as head teacher of failing Adderley Primary school in Saltley yesterday, also expressed concern.
"You can start to make a difference and change some systems in a year, but to turn a school round from being a failing school to a good one will take five years," he said.
Ms Kelly quoted Ofsted's chief inspector of schools David Bell's assertion that if a failing school has made no progress in a year "it is unlikely to happen at all".
But union leaders claimed the measure was designed at paving the way for the Government to achieve its target of increasing the number of city academies from 17 to 200 by the end of the decade.
Steve Sinnott, general secretary of the National Union of Teachers, said: "We have seen the armtwisting of local authorities across the country to include academies in their plans for school development."