Schools are expanding their use of CCTV to monitor teaching performance and "private" spaces, including toilets and changing rooms, the UK Government's privacy watchdog has warned.
Video surveillance has moved from being used for security to keeping check on pupil behaviour in all parts of schools, according to a report by the Information Commissioner's Office (ICO).
The growth of "private sector management" of state schools is also likely to herald a new wave of privacy issues, the report says.
The wide-ranging concerns have prompted an angry response from unions, which claim that cameras are being used to undermine their members.
Chris Keates, general secretary of the NASUWT, said CCTV was "crude and ineffective".
"The increase in CCTV surveillance of teachers can be correlated directly with the increase in school autonomy and the punitive accountability regime," she said.
Mary Bousted, general secretary of the Association of Teachers and Lecturers, said: "Many schools have CCTV, but no CCTV policy, and in that vacuum anything could happen. Everyone should know where the cameras are and what they are being used for."
The report, which includes contributions from academics at the Surveillance Studies Network, was presented to the Westminster Parliament by information commissioner Christopher Graham. It says: "The use of CCTV in schools has migrated from perimeter security and access control to monitoring pupil behaviour in public areas, such as in corridors and playgrounds, and to more private realms such as changing rooms and toilets."
It adds: "As the function of school CCTV has changed, it is apparent that some schools have not understood their new regulatory responsibilities. These issues are only likely to intensify with new uses for cameras in education, such as the remote-operated web-cams on laptops provided for pupils' home use in the US. Similar practices are more likely in the UK if private sector management of state schools spreads, as the Government intends."
David Smith, deputy information commissioner, said that CCTV should only be used to monitor pupils' behaviour in exceptional circumstances.
"We would stress that constant filming and sound recording is unlikely to be acceptable unless there is a pressing need," he said. Constant CCTV monitoring of whole classes as a means of combating "low-level disruption" would not be justified. Despite this, the report notes that complaints to the ICO have risen in the past year.
"School teachers, in particular, have found that CCTV installed to control pupil behaviour has been used to monitor their teaching performance," it notes.
The report comes after a study funded by Salford University, published earlier this year, which found that surveillance cameras are now installed in most UK schools.
Dr Emmeline Taylor, the author of that study, said that the ICO was powerless to punish schools that broke the rules. She is calling for bespoke guidelines on CCTV for schools.
A Department for Education spokesman said: "We expect schools to comply with guidance from the Information Commissioner's Office. The Coalition government has committed to regulating CCTV. This will apply to education settings."