For quite a while, people were told that in the event of a shooter, you should all gather in one room and hide. This strategy was found to be very inadequate. I believe most training now is: if you hear shots, everyone should run and scatter and get away in any way you can. And fight if you have to.
That's not bad advice.
But I'd like to see a little more emphasis on the fighting. As in: if you are in a room with the crazy guy with a gun, fighting should be a top priority. Waiting and hoping for a good outcome should not be a top priority.
But our current culture doesn't tell people that violence can lead to a good outcome. "Nothing was ever solved by violence". And so many people act like sheep rather than fight.
After the Columbine shootings the “words of wisdom” was to huddle together, stay in place. My daughters were in high school and I told them not to do that unless they wanted to die. I told them their real choice was to flee or fight and it depended on the situation which would be best. I have no idea who the genius was that thought students should stay in place or huddle together. Sure make great targets that way.