Exactly.
People have to keep this in mind. This isn't an iPhone or Mac, but an AirTag with a throwaway price.
I personally wouldn't knock on doors, get the school involved, definitely not the police, for $30. Currently the price of an AirTag is $22.25 each for the 4-pack on Amazon.
It wouldn't be worth the effort and hassle.
Plus, you may look like you are accusing someone of stealing, when they could have just found the AirTag, making a tiny problem into a big one.
It sucks you lost the AirTag, but I would just consider it that, a loss. This doesn't mean you can't keep an eye on it, see if something changes, but I would just leave it at that.
BTW for the people saying to contact the police, I am unsure of what the police are like in your area, but everywhere I go, they are way too busy to deal with stolen iPhones, let alone something that costs as much as a few coffees from Starbucks.