Several US schools to install pepper-spraying drones to respond to school shootings
(www.theguardian.com)
They're not that easy to hit. I once invited someone to try hitting my camera drone with a 9mm and they couldn't, despite all bluster and claims otherwise. it might have been easier inside a building.
But, any rounds expended toward the drone are rounds not sent to children/staff. And an FPV drone to the face even without pepper spray can mess up someone's aim.