I remember when Columbine happened, I was in my final year of high school. There weren't any drills at the time for that sort of thing, but soon after I graduated, my younger brother (who was still a student at the time) told me that there was an incident where someone (probably not a student - there was a lot of violence between my school and a rival school in an adjacent suburb) was seen running through the halls with a sword, and after that, they instituted lockdown drills.
Interestingly enough, in 2005, there was a shooting, and a few years later - 2008 I believe - there was a stabbing incident.
It's kind of disturbing to see violence escalating like that.
(Chinguacousy Secondary School, in Brampton, ON, in case anyone was wondering.)