Something to consider-
I know it has been brought up already, but you would likely be assumed to be the shooter if you were in the school with a gun drawn unless you were dressed like an undercover.
Personally, I would appreciate anyone who neutralized a person targeting my students, my personal children, and/or my colleagues and me; however, I can also see where this could end badly for the good Samaritan.
"If a man breaks in your house, he ain't there for iced tea." Mom & Dad.
The NRA & TSRA are a bargain; they're much cheaper than the cold, dead hands experience.