Instead of in the Funny Pictures Thread, I thought we might be able to have the discussion here.
With your answer, you are assuming that there is only you and the bad guy, how about adding more people/students to the mix?
Now please remember, there are an average of about 21 people in a classroom at one time, in most schools. Since this is hypothetical, the gunman comes in and takes out the teacher, several students run out, now the gunman has 15 students left. The protector is gone, the concealed weapon on the teacher is useless, the students have nothing to do but get shot or fight with whatever they can use.
Now, since the students have a can of peas, they have a chance to protect themselves, because the gunman can ONLY engage one target at a time, giving a few precious seconds for someone to hurt/distract/knock out the gunman. This also gives time for more students to get out of the kill zone.
Lets discuss this topic civilly, no name calling, no bad mouthing, etc. Keep it clean and open.