I'm all about controlled entry points and School Resource Officers (SRO's--uniformed, sworn LE assigned to the school) but at least in Bellevue, the financial resources aren't there, except at the high school level. And a little anecdote...when I was still married, and my husband was a principal at a HS, he had a parent walk into the school, walk right past the SRO's office, walk into his office, take out a pistol (no idea what it was, other than a revolver of some sort), lay it on his desk, and ask my now ex-husband why, exactly, he (the irate parent) shouldn't shoot him.

My ex sat there for a moment (okay, he's a lot more mild-mannered than I am), stood up and said, "Felony charges?". Guy started laughing, holstered his pistol and just then the SRO came in. The man was arrested without incident (I can't remember the exact charge, but I believe it was along the lines of brandishing a weapon).

In the mass shootings, it's always the principal and the SRO who are taken out first, or at least it seems that way to me.