The problem is so widespread that the schools technology agency, Becta, has set up a working group with the Metropolitan and Greater Manchester police forces, the Department for Education and Skills, local authorities and suppliers to combat the crimes.
In the first quarter of 2005, there were 195 school break-ins involving the theft of projectors in London. One local education authority in the North-west, which did not want to be named, lost 130 projectors in three months last year.
The devices are worth up to pound;1,000 and are popular with thieves as they can be carried off in a shoulder bag. The projectors are similar to those used in pubs and can be linked to TV sets, video recorders or computers to project on to walls.
Mark Wallbank, head of procurement at Becta, said schools often failed to use appropriate security devices. "Many projectors will not work when plugged in without a PIN code," he said. "But many schools don't bother."
Hallfield junior and infants, near Kensington Gardens, in west London, has had seven projectors stolen in five break-ins.
Judith Grigg, head of Hallfield junior, said the school had fitted protective metal cages around its projectors after the first break-ins.
"The next time, they just took the projectors and the cages," she said.