At my old high school? Lets, see, we had a 2 bombs scares, a shooting threat and a couple of chemical leaks resulting in 3 class rooms being closed down for "Clean up."
The fun part is, they never evacuated the school during the bomb threats, they brought in a K-9 unit for the shooting threat, but didn't hinder classes and they did a piss poor job of cleaning up those chemical messes.
Oh, and that was just my Freshman year. Life Lesson here people, don't send your kids to inner-city public schools.