Schools have installed CCTV cameras and microphones in classrooms to watch and listen to pupils.
The Big Brother-style surveillance is being marketed as a way to identify pupils disrupting lessons when teachers' backs are turned.
Classwatch, the firm behind the system, says its devices can be set up to record everything that goes on in a classroom 24 hours a day and used to compile evidence of wrongdoing. The equipment is sold with Crown Prosecution Service-approved
evidence bags to store material to be used in court cases.
Data protection watchdog the Information Commissioner has warned the surveillance may be illegal and demanded to know why primary and secondary schools are using this kind of sophisticated equipment to watch children. Officials said they would be
contacting schools to seek proper justification for the equipment's use. A spokesman said the system raised privacy concerns for teachers, students and their parents. The use of microphones to record conversations is deeply intrusive and we
will be seeking further clarification on their use in schools and, if necessary, we will issue further guidance to headteachers.
Classwatch is set to face further scrutiny over the role of Shadow Children's Minister Tim Loughton, the firm's £30,000-a-year chairman.
The systems cost around £3,000 to install in each classroom or can be leased for about £50 per classroom per month. The firm says the devices act as impartial witnesses which can provide evidence in disputes and curb bullying and
unruly behaviour and protect teachers against false allegations of abuse – plus provide evidence acceptable in court.
Schools are required to inform all parents that microphones and cameras are monitoring their children.