There is no real solution.
Arming teachers?? Most teacher are mild mannered to begin with and most have likely never held a gun or shot it. Also, the first thing I think of with this solution is classrooms would resemble Gulags or North Korea camps where the kids go to school but they are just taught by guards rather than teachers.
Also so best case scenario of an armed teacher is a shoot out between teacher and student? Around other students? I have noticed that school are almost on constant lockdown and every door is marked with a number. Not sure the point of door numbering. When i was a kid, people just walked in and out of school. I had major discipline problems when I was younger, I no doubt would be expelled from school these days. I would tease the foreign exchange students like crazy, tell teachers I am taking over the classroom, randomly punch those dumb ass Indian kids, etc. Hell I would probably be targeted by a school shooter. Haha
Social media is the reason for alot of this crap and also of the millenial problem. These days, you have 10-12 years from birth to raise your kids and then alot of it is out of your hands. I don't know why 12 year olds need smart phones. When I was 12, the only peole I knew outside of family were some kids on the block.
When I was a kid, we had video games and you played them with friends but these days even sitting at home playing video games, with these headsets kids are interacting with complete strangers.
Such a different and more fucked up world. If I were a parent especially to a girl, smart phones and internet access would be monitored even if they bought the crap themselves. Not hard for a kid to save up for a computer or a phone if that his only expense.