I always had some sort of pocket knife on me as well in middle school/high school. Never had a problem, but I was always good with knowing when to use it, and when not to.

In high school one of the teachers started an adventure club/camping club. So we would go to the meetings after class was over for the day, to work on different skills and such. I remember in one of the early meetings someone asked if anyone had a knife or scissors to cut some rope for knot practice. Well, near half the students in the club offered up a knife of some sort, as did the teacher (who, we later learned, always carried a large SAK).

We're not talking about a dangerous school in a bad area either, I went to a private high school in a well-off area. It was kind of funny to see ~15 guys in suit-and-tie offering their pocket knife. It seemed as though many of the guys thought it was very gentleman-like to be able to offer up a knife or lighter to someone in need, so they always kept them in their jacket, just in case.