WOW, I don't know what to say. 99% of the times it's just some moron kid, playing games, sadly the playing dead is right, if the gunman is close by. If not throw a desk/chair anything out a window and get out. Once in view of any officals keep your hands up and in view at all times, remember they don't know who the good ones are and who is the bad guy, they all just look like kids.
If wounded or hurt, try to control all bleeding with direct pressure, Saftey above all else, but if able to stay still and if wounded or hurt, control any bleeding and lay flat with legs raised on a chair. If there is still a danger, control the bleeding with direct pressure and get out as quickly as you can.
Use any means to contact the police, if in school and no phone is around, pull the fire alarm, the police will respond to any report of a school fire right away. If unable to get out, find a hiding place and keep low and quiet!! Dont be a hero!! If in immedaite danger and have no escape route, use fire Extinguishers as a weapon, if filled with foam they will cause the eyes to freeze and burn on contact, also will cause a few minutes of loss of vision.
It's so sad we need to discuss this. I'm sure all will be ok, some punk kid playing games.