If I was the principle for a school I would have a safety plan for my school just in case a tornado hit the school my plan would be to have every one move into a classroom with no windows or the room is not on the outs side walls. We would move to this room and tell them to get in a designated corner as soon as a tornado was spotted we would stay there until it is over if. We would have a pre recorded message to call every parent if we had spotted a tornado.
We would let all the parents know that there kid will be ok and we would not release them until the tornado is gone. During a sporting event, like a football game we would have a teacher who is running the concession have a computer with the weather forecast in the room to be able to run out and tell every body that a tornado is coming if one might happen to appear while the game is going on.
We would have all the parents and athletes move into a gym of a few classrooms in the center of the building. This plan should take about 5 to 10 minutes to get every body inside. We would reschedule the game to later day. We would hold people for 15 min after the storm is gone to make sure that the cost is clear. If we happen to have a storm that last all night we would release the parents at the safest time possible.