I think it's PAST time. I think 'properly trained' teachers should been given the option of being discretely armed.
When I was an LEO, I was also a full-time teacher. Immediately following 9/11 I was armed at school (SIG P230 in an ankle holster) every day. This was waaay before SROs. I wasn't worried about 'terrorists'. I was worried about the local 'nut job' (every town has one or two) wanting his '15 minutes of fame' before the world ended.
My current school has 1200+ students, is well over 200,000+ sq. ft., and occupies BOTH sides of the street. There are 73 separate entrances, and ONE SRO. Yep. One.
When TSHTF, teachers ARE the 1st Responders.