A London secondary sent all its pupils home this week when temperatures in its classrooms topped 30oC.
The 1,350-pupil Pimlico school, built in 1970,Jis a top priority for replacement, Westminster council said last month. The school's last Ofsted report rated its accommodation problems as "urgent", saying the heavily-glazed rooms were too hot and too bright in summer.
"It is a great glass conservatory," said Mair Garside, the school's chair of governors, who estimated that 1,200 pupils had been sent home. "They've been talking about rebuilding the school for such a long time, and it's something that can only be put right with a new building."
Fir Vale school in Sheffield, south Yorkshire, drilled large holes in two classroom walls to provide emergency air-conditioning.
Neighbouring Tapton school is spending pound;15,000 out of its education projects budget on six air-conditioning units. It has been shuffling pupils between rooms to avoid the stifling heat.
Many schools sweltered in this week's heatwave. Heads said that changes to the designs, ventilation and air-conditioning, demanded during the 2003 heatwave, have not materialised.
If classroom temperatures drop below 180C in winter, government regulations allow heads to demand that the school building's owners take action; or else they can send students home.
But when temperatures hit their summer highs, and the Met Office predicts they will remain high during the next two weeks, similar sanctions do not apply.
The Health and Safety Executive said its regulations required that workplaces should not drop below 16oC, and not rise above a "reasonably comfortable temperature". But regulating a maximum school temperature was a matter for the Department for Education and Skills.
A DfES spokesman said that it provided clear guidance on ventilation and other issues for schools, but not a maximum temperature. He said dealing with high temperatures was a matter for the local authorities.
Tapton school was opened five years ago under a private finance initiative contract with property manager Interserve.
Ever since then, Interserve had been "locked in a wrangle" with the local education authority over responsibility for flaws, including upstairs classrooms that overheat, according to David Bowes, Tapton's headteacher.
He said: "The windows do not open wide enough, and it's almost impossible to dissipate the heat. We have known about this problem for five years.
There is a powerlessness that comes with being part of a PFI contract.
"A regulatory maximum temperature would help a good deal, but there's probably not a hope in hell of getting one in the legislation, because many public buildings could never comply because of their poor design."
A report by the Commission for Architecture and the Built Environment said that nearly all schools built in the past five years failed to tackle basic issues of environmental sustainability such as providing natural daylight and ventilation. The government advice body was particularly critical of schools built under PFI contracts, saying they comprised nine of the 10 worst schools in its audit.
Richard Simmons, the organisation's chief executive, told MPs that one school built in the past five years has such narrow corridors that it has had to impose a one-way system. Another had a library with no windows, while another has a glazed roof that gets so hot in warm weather it has to be sealed off.
Michael Lewis, head of King Edward VII school in Broomhill, Sheffield, said his pupils had no prospect of relief until the weather cooled: "When the temperatures rise to exceptional levels - and they are exceptionally high at the moment - then youngsters don't feel very well."
The National Union of Teachers called for the Government to regulate a maximum school temperature of 24oC, consistent with World Health Organisation guidelines.