You slow it (because you’re never going to stop it) is by making schools hard targets by arming teachers, faculty, and whoever else is willing to do active shooter training. There are also PLENTY of retired cops, military and special forces who would be happy to serve. Things like this should be mandatory in every school district in the country. These fucking schools were given over $100bil in Chinavirus relief and it was hardly used. It doesn’t cost that much for each district to put these plans into place.
American schools are going to become even more like prisons, with high walls, secure gates, and "papers please" type regulations. And then you'll be shocked when more kids grow up to be shooters and lunatics. Schools are already hardly distinguishable from prisons.
And what do you think that people mean when they say "increasing mental health screening?" Dude, this shooter apparently had no criminal history at all, and no obvious or outward mental health issues. What they'll want to do -- and indeed the only way it would work -- is dig in to your online history via your ISP, and want to find out if you've ever posted on /pol/ or in a Matt thread on GetBig.
If you're a normie with a facebook account, cool. If you're a weirdo with 10,000 posts on GetBig, well... "Denied for mental health reasons."
You in particular should be VERY skeptical of "mental health" initiatives.
As for arming every adult in schools: I agree that it's probably the best option.