NO! ABSOLUTLY NOT, in THIS case! The kids had just left the room - he knows who his students are, they heard the shots and screaming and ran right back to THEIR classroom. There was NO shooter with the group, as the shots were heard a distance away. So, that teacher is a complete ahole AND coward. There was NO reason not to get those kids back into the classroom and then lock the door, protocol or no protocol!
The teacher did the RIGHT THING!
(see, you're not the only one who can shout.)
You may be right, of course, but in that kind of situation, no one knows if there are multiple shooters, where they may be, etc.
I think that a frantic beating on the door and the student’s voice could be assessed in determining the situation.
But as horrible as it seems, if students were shot at his door, he probably made the right decision.
Definitely, people with guns ready are needed in these schools.
I think all the venom needs to be directed at the sheriff and the corruption associated with his policies, and the dereliction of the FBI. They made it all possible.