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By the way: it might not be a good idear to take pictures of your students holding paper wallets... If somebody is able to read the private key, or restore the qr code, they can rob your students, unless you used encryption and a strong passphrase...
I really doubt that some scammer/criminal will be patiently waiting for those people to post a picture holding their private keys,in order to rob the satoshis,that are sitting in their wallets.What's the point of robbing a few satoshis?It doesn't make sense.
Anyway,I think that OP has access to free electricity,provided by his school,so there won't be a problem to mine a few satoshis,by using old mining equipment,even though the mining won't be profitable.
We desperately need more Bitcoin teachers around the world.
Good luck with this project.