Electronic key card locks

Never installed them but the ones where I work run off my infrastructure. I'm sure you could retrofit the doors. All that's really going on is a card reader reads the card, sends the info back to a central server over cat5 ethernet, the central server logs the requests, and either approves or denies entry. This sends a signal back to the door lock, often an extremely powerful electromagnet, and allows the door to be opened.

All of that could be done fairly easy as it is just cable to be run.

There are other issues involved. Typically there is an internal motion sensor to allow people to exit without swiping. Also safety regulations I'm sure, like in the event of a power outage, they probably have to fail open.

Cheaper to do Dad Defense....each one of you takes a day off and sits outside of school all day.

I'm no security consultant, but I think the types that have shown to attempt what you want to avoid would be more apt to not try with a live person standing watch.

Not wanting to hijack, but my kids go to a similarly arranged school and interested to hear if I'm nuts- I've considered starting this for a while- I understand there are some schools in CA that already do it.