Fingerprints of one million children have been recorded by their schools, prompting criticism from a civil liberties group.
Big Brother Watch used the Freedom of Information Act to ask schools if they were using biometric technology.
It allows children to use their fingerprints for things such as taking out library books or paying for lunch without cash.
But the campaign group said a third of schools did not consult parents before taking the fingerprints of their children.
The government changed the law last year to allow parents to opt out of giving their children’s biometric data.
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Nick Pickles, director of Big Brother Watch, said: “As the new school term gets under way, now is the time for parents to check if their children are among the hundreds of thousands of pupils who are using biometric technology.
“Going to school should not mean kids are taught they have no privacy, especially at a time when we are sharing more data about ourselves than ever before.
“Fingerprinting them and tracking what they do might save some admin work but the risk is pupils think it is normal to be tracked like this all the time. Schools need to be transparent about what data is being collected and how it is used.
“Parents will be rightly concerned to hear so many schools did not seek their permission to fingerprint their children, while pupils may not have been made aware they now have a legal right to ask to use a system that doesn’t require a fingerprint to be taken.
“The Government was right to change the law but it’s up to parents to make sure the law is being followed.”
A Department for Education spokesperson said:“It is absolutely right that parents should decide how their child’s personal data is used.
"That is why we changed the law so parents now have the right to prevent schools and colleges – including independent schools - using their children’s biometric data.
“Schools and colleges must now ensure that written consent is obtained from parents before a child’s biometric data is taken and used, and must make alternative arrangements if the request is refused.”Subscribe to our Newsletter