Allow the CDC to study gun violence, allow the ATF to track sales of guns, create FBI task force specifically to curtail mass shootings. I used to have a few friends in the OSBI and one told me that once 9/11 happened everything was counter-terrorism and they were pulled off their specialties. I would create a dedicated department for this and have them work closely with the ATF. Make private sales illegal since there are already 3 million or so AR-15's out there. More extensive background checks of course.
But the thing about banning types of guns is that you have to legally define what you want to ban. Once you do that it's pretty easy for the manufacturer to get around those definitions. So banning things won't work. We need regulation, better vetting and tracking of sales.
As far as arming teachers...that has to be the single dumbest idea I've ever heard. They can't fund schools here in Oklahoma enough to even have a 5 day school week and now they're supposed to fund training teachers, who by the way many people treat as surrogate parents expecting them practically raise their children, and now they're supposed to train to potentially engage in a fire fight??? My mom was a teacher, I have teacher friends and have spoken to a few about this. They've all said they will find another line of work if they are asked to do this (yes I know it's anecdotal evidence). But I have not heard of a single teacher that is enthusiastic about this idea.