Knives can be used as tools, such as an eating utensil. A stone on your desk can be a paperweight, or thrown as a weapon. This is a total lack of common sense.
I remember one day in Jr. High, word got around that a science teacher who was an amateur archeologist, collected old military weapons, uniforms etc.. He brought in a WW-II Thompson sub-machine gun and we all went to his classroom to look it over and hold it. Imagine that today.
The public school systems today are run by people who have no common sense to make the slightest adult decision. They're imbeciles.