+1 I think blaming the students is a cop out. How unsafe is your class? You can still die if shot wearing body armor.
I'm along the line that if a student wants a vest they should have brought one.
You can do everything in the world to control the situation but you CAN NOT control people.
It is impossible to be able to get to everyone on the line faster than they can take an incredibly stupid action. How long does it take a person to turn a gun 90 degrees and pull the trigger?