I know times have changed in the 47 years since I was in high school but it was not uncommon for us to bring a scout knife, a b.b. gun or even a hunting rifle to "show and tell".  This was in the 50's for grade school that we had show-and-tell but all the same, we did bring those kind of items without a problem.  We just had to keep it in the closet before and after show-and-tell time.  

Even in 1971 I brought my pellet rifle to my physics class at LCC because we were measuring bullet velocity.  As I recall, I just needed to keep it in my car until class time.    

I can't ever remember a time that we would have considered using it against anyone.  We brought it because we were proud that we had this new possession and wanted to show it off.

As I said, I know times have changed but the item is not the problem, it's just how people have chosen to use it that has changed.