Answer:
Easy what you should do in a lock down you should leave through any available exits. If there aren't any then you should get somebody and barricade the doors. If you don't have enough time then you should grab something big or something sharp to defend your self if he comes in. If you have found an exit by then you leave around a mile away from the building and call the cops. On your way leaving encourage others to come with you and if you see anybody heading toward the building tell them don't go.
Step-by-step explanation:
Thats how to survive shooting or lockdown. :)