The type of scanners used in schools don't take or store any sort of "fingerprint" in their systems. It simply changes a few key markers into a form algorithm only recognizable by the system that created it. It cannot be used or re-verse analyzed to produce anything that would lead to the identification or verification of that person.
Not true - there is research (e.g. cited above) indicating that "reverse construction" of at least partial fingerprint data from stored markers may be possible.
Plus, I found that biometric scanners are more secure than using PINs or ID cards.
Why on earth does an adult woman need a more "secure" way to pay £3.50 for a school lunch than just pulling some cash out of her purse? In particular, why does she need to use a system that allows her employers to store data on what she eats?
But don't rely on me. There is a wealth of reputable information on the web and through third-party research firms around the world.
The only "firms" conducting research in this area are those with a commerical interest in the adoption of biometric technologies.
Your wife's fears are not simply not grounded in anything but fear of "big brother", as were mine, and now I am a fledgling convert...
A convert to unnecessary and intrusive use of biometric identification and data retention.
There are real things to fear here...
e.g. you could be hauled off to a police station for questioning because a partially reconstructed fingerprint derived from your biometric record matched a scene of crime print.
Or you might receive lower priority NHS treatment (or more expensive health insurance) because the data recorded on your food choices suggested an "unhealthy" diet.
They might seem far fetched now - but stuff like this is on the cards.