More than a million children have had their fingerprints taken at school, it has been revealed.
Fingerprint-reading equipment - used in canteens and at registration - allows teachers and some parents with online access to monitor whether a child has turned up at school, what classes they have attended, the food they have eaten and the library books they borrow.
Around two fifths of secondary school pupils had given the so-called biometric information by the start of the 2012 academic year.
But many were not told they could refuse, according to the campaign group Big Brother Watch.
Big Brother Watch, which used Freedom of Information requests to uncover the scale of the practice, fears the information will be kept on school databases or by third-party organisations such as the IT firms that supply and maintain the systems.
In fact, it should be deleted when a child leaves secondary education.
Director Nick Pickles urged parents to ask headteachers whether their children's details had been recorded secretly.
He also warned that pupils were being conditioned to take the loss of their privacy for granted.
He said: "Our major concern is that if you introduce children to providing a thumb print and being tracked across different services, they will be conditioned to think that is normal.
"That should ring alarm bells for parents and anybody who wants a civil society with proper boundaries for privacy.
"Parents will be rightly concerned to hear so many schools did not seek their permission to fingerprint children, while pupils may not be aware they have a right to use a system that doesn't require a fingerprint."
Around 40 per cent of English secondary schools were using biometric technology at the start of the 2012-13 academic year, with an estimated 1.28million pupils on databases.
The survey of 1,255 schools found 31 per cent had not bothered consulting parents before they were legally required to.
A Department for Education spokesman said: "It is absolutely right that parents should decide how their child's data is used. "Schools and colleges must ensure written consent is obtained from parents before a child's biometric data is taken and must make alternative arrangements if the request is refused."