I had the misfortune of experiencing the beginnings of this transition as I went through school. When I was in cub scouts, I carried my swiss army knife in my pocket in school - I knew it was technically against the rules, but my teachers also knew I was in scouts, and as long as I wasn't waving it around at the other kids, they didn't say anything about it.
I still had no problems carrying the swiss army knife when I made it to seventh grade and was taking shop class, but again the understanding was that it was to be kept in my pocket whenever I was outside of shop class. I followed that rule, and had no problems.
By tenth grade, when I was taking more advanced shop classes, electronics and so forth, the swiss army knife was sitting in a drawer at home. The school instituted first a "three strikes" weapons program, and by graduation they had a "zero tolerance" policy.
This is a school that, to this day, has a strict rule in place that teachers cannot schedule tests during the first week of deer camp, because somewhere between a third and half of the male students will be missing. Yet they still gave in to this goofy paranoia.