Schoolchildren are using social networking sites during lessons and are coming into school tired after using the web late at night, according to a survey by IT consultancy Global Secure Systems (GSS).

More than half (52 per cent) of 13-to-17-year olds admitted to using sites such as Facebook during lessons, and 25 per cent said they do so for at least 30 minutes a day.

Schools are facing a big challenge and must take action, said Toby Mullins, head of Seaford College.

"There are two main issues: one is the safety of youngsters on the web and the second is the time that is frittered away. The time youngsters spend on the internet, and more specifically on social networking sites, is a huge challenge for parents and those of us in education," he said.

“Youngsters are not only using lesson time but often quietly continue late into the night, leaving them short of sleep and irritable the next day. We now need to plan for a solution."

Schools should realise that there are effective ways of curbing the problem, said David Hobson, managing director of GSS.

"Kids are potentially wasting as much as two and a half hours a week of lessons on Facebook. Schools could learn from industry and ensure children productively use the internet. Using software, access to inappropriate webs ites can either be completely blocked, or limited to break time economically and efficiently," he said.