Either, or both.
If they're not used for killing, how are they used?
You would have armed teachers if you had as many idiots as we do.
Generally, teachers aren't the ones who should, or want to be armed. They're usually against guns & violence, even if what they teach/promote leads to it but that also depends on location- in a place where safe gun use & handling are taught early, sure but in cities where people aren't exposed and they shake with fear as soon as they see a photo of guns, you don't want them carrying in school unless and only if they are interested, receive a lot of raining and practice frequently, so they can handle violent incidents without becoming Don Knotts as Barney Fife or The Shakiest Gun In The West.
There's no way school shootings should be easy, or even possible. In Uvalde, many people f%cked up and caused 21 deaths & terrible emotional distress. There should be no way someone can enter without the correct credentials, whether an ID card that's swiped at the door, keys, RFID fobs, I really don't care how they secure the places, I just want them secured. The largest glass panels and any glass near doors should be impenetrable, whether by impact with objects used by a shooter/burglar or from gunshots. If it requires multiple layers, so be it. Doors need to lock automatically and be unable for that to be defeated but they can't be locked from the inside because that's how people die when a fire or other incident causes people to stampede.
If you extrapolate the Swedish population and the ratio of gun deaths to people stays the same, Sweden would have had 5024 last year in the link's info is accurate (157 last year).