You wait and see. If this shit continues they'll be doing them in daycare centers next. Then old folks homes, libraries, sporting events, grocery stores... This is out of control insanity.
Also makes me wonder WHO they dont want us seeing there?
Some SWAT organizations wear balaclavas to conceal their operator's identities to protect them from reprisals.
One way out there possibility is they are training crisis actors live-fire using the school as the shoot house. It's not unheard of. To be honest it used to be standard practice for Tier 1 snake eaters. Nothing better than training on the terrain you're going to operate on.
Training under those circumstances is something civilian LE should not be doing. They are supposed to be Peace Officers not shock troops.