Yes, I summarized because I think spending time to look for a weapon is pretty close to a no win scenario. Perhaps a teacher could quickly search the classroom for things to throw at the intruder. The reality is in pre-school or grade school classroom, someone with a gun comes into the room the teacher is going to be immediately surrounded by 28+ scared children. What teacher would leave them unprotected by going to get something to throw? (Oh and things dangerous to adults are usually more so to young children.)
Sorry but your, think fast, look for a weapon approach is flawed. There is no time to do so. Not an expert but it would seem 3-5 seconds at most before bad things start to happen. Only thing I have to throw at the intruder is me. That's what some teachers in Newton did. Not a very successful strategy.