The link below speaks of training on the topic of active shooters that is being provided to area schools. The concept is a simple one.
1.Communicate to staff and students any known information. The gunman knows what he is doing as well as his location. Forget about silly codes and provide the innocent with useful information.
2, If there is a chance to get out of the building, do so.
3. If evacuation is not possible barricade the door with what is available.
4. If all else has failed, fight back.