Teachers have also claimed to have suffered ill effects, including headaches, nausea and heart irregularities, which they blame on the “wi-fi” technology.

More than half of all schools had wifi networks in 2004 and the number has continued to rise.

Ian Gibson, a Labour MP and cancer scientist, has asked the Department of Health to commission an investigation into the effects of wi-fi networks on children’s health. But most scientists said fears are without foundation.

Doctors have approved the use of a wifi network at Great Ormond Street children’s hospital, so children can keep up with their schoolwork on laptops.

Dr Michael Clark, science spokesman for the Health Protection Agency and a member of its electromagnetic fields discussion group, said classroom measurements showed wi-fi networks issued no more radiation than radios or TV transmissions.

But if schools were concerned, he said, they could discuss installation of networks with parents or exercise caution by placing transmitters in corridors.

Wi-fi opponents acknowledge there is no direct scientific evidence of ill effects but argue that it should be treated with caution until it can be conclusively proved safe for use.

Philip Parkin, general secretary of the Professional Association of Teachers, said: “I’m not saying this technology - which has many educational benefits -should be banned, but more research and proper safeguards are needed.”

Michael Bevington, who has taught classics for 28 years at Stowe, a private boarding school in Buckinghamshire, said he began suffering headaches and other problems after wi-fi transmitters were installed in his classroom and near his study in September.

The school has now removed the three nearest transmitters. “I went to the head and said I couldn’t continue teaching unless the transmitters were removed,” Mr Bevington said.

John Fox, a maths teacher at the private Birkenhead school near Liverpool, said he had first fallen ill when he installed a home wi-fi network, and then again when his school set a system up. He approached the headteacher and had it removed.

At Ysgol Pantycelyn, a comprehensive in Carmarthenshire, governors bowed to parents’ demands and switched off the wi-fi network.

And Vivienne Baron, who works with anti-mobile phone mast lobby group Mast Sanity, led a delegation of parents who forced the removal of a wi-fi network at her grandson’s preparatory school in Chichester’s Prebendal school.

“If children become ill - as they eventually will - then schools will find they are not covered by insurers because this technology has not been proven safe,” she said.

The Department for Education and Skills said it stood by the all-clear verdict given to wi-fi by the Health Protection Agency.