Most schools use CCTV and one in 10 even have their toilets under surveillance.
Some 85 per cent of 250 primary and secondary teachers polled said their schools use surveillance cameras, according to research from the Association of Teachers and Lecturers (ATL).
The survey showed that over half of teachers felt safer for having the cameras, but nearly a quarter were worried there schools featured hidden cameras they weren't being told about.
The majority some 98 per cent said CCTV was used mainly for security, with another three-quarters saying it was used to prevent vandalism. But half admitted it was being used to monitor students' behaviour.
While the majority of such cameras are at entrance doors, one in ten teachers said toilets were also under surveillance. And, seven per cent said CCTV was being used in classrooms.
Nearly one in six said their school had over 20 cameras.
"No-one really knows enough about the use of CCTV in schools - it's a very new issue," said Dr Mary Bousted, ATL's general secretary, adding that the body had set up a working group on the topic and will produce guidelines for schools and colleges.
She said staff should be involved in decisions about how CCTV is used in schools, and its use should be strictly controlled.
"Although surveillance in schools can have some positive outcomes, such as discouraging vandalism and violence, we think there are some instances where it should be strictly controlled," Bousted said.
A report released last year by the Royal Academy of Engineering warned against potential for misuse with CCTV.
