[HarryD]

Took active shooter training last year. My take away:
1-Get out if you can do so safely;
2-Hide if you can be unseen;
3-Attack aggressively with what ever weapon or thing you can lay your hands on. No warning just attack until the shooter is rendered incapable of further action or you are stopped by a responder. At this point it is him or you. Make it you.

Be aware that the responders are not there to rescue you or render aid, only to take out the shooter. Rescue will come later.

I have noticed that the responders response has changed from slowly securing everything, negotiate etc to a fast tempo of getting there, set up, and find the shooter.