Government plans to deliver thousands of energy-efficient schools could be threatened after recent studies showed the new buildings are making pupils drowsy and less attentive in class.
Two reports by Reading University and University College London show that new schools, designed to be more airtight to reduce heat loss, are also poorly ventilated, which results in higher carbon dioxide levels.
According to the studies, high CO2 levels in classrooms lead to children becoming sleepy and less capable of taking in information.
The news will come as a blow to Ed Balls, the Schools Secretary, who wants every new school to be zero-carbon from 2016.
Dr Dejan Mumovic, a lecturer at UCL, told The TES: "Although the school rebuilding initiative is a fantastic one, the Government has rushed its sustainable schools programme a little bit. We monitored 10 schools that were built 50 years ago, then nine schools built under the Building Schools for the Future (BSF) programme and found nothing had changed - the ventilation rates were equally appalling. CO2 levels are exceeding targets, and that can affect the learning performances of kids."
Professor Derek Clements-Croome, a research director at Reading University, ran similar tests at eight primaries.
"We tested reaction times and memory of pupils," he said. "When the CO2 was very high, the reaction times would slow and memory would be affected. The kids would also get drowsier.
"A classroom doesn't have to be that small if you have 25 children and a teacher breathing in and out and the proper ventilation isn't there.
"You may not even detect that it's getting stuffier in the room. But once higher CO2 levels are breathed in, it gets into the blood and goes to the brain.
"People are trying to get their energy consumption down, but that shouldn't be at any expense. There is no point pushing for energy reduction if kids are falling asleep."
The Commission for Architecture and the Built Environment, the design watchdog, said sustainable school design should mean a comfortable environment for all.
Rachel Toms, the commission's senior design adviser, said: "Good ventilation in a school can be challenging. Heat loss in winter needs to be minimised, but at the same time there must be enough fresh air to maintain good oxygen levels and avoid excessive CO2 in the intensively populated environment of the classroom."
In September Robin Nicholson, the man in charge of the zero-carbon schools programme, told The TES it would be "bloody difficult" to achieve the 2016 target.