These are just the thing that administrators like so that their jobs will not require any thinking (never mind the possibility of creative thinking).
In reference to a case where a 12 year old was expelled for bringing his own scissors to a sewing class Jim Peacock at Zero Intelligence (a new blog devoted to zero tolerance issues) writes:

Scissors, in Home Economics class, are a weapon and posession of them requires expulsion? We’ve gone from “Don’t run with scissors in your hand” to “You can’t come to school if you use scissors”. Scissors are not a weapon. They are a tool, just like a chair or a pencil or a pointer or the cord from the window blinds. All of them have proper uses and all of them can be used to hurt another person. In fact, can you think of any common scholastic item that can’t be used to hurt somebody?

The full story is here.
Via Overlawyered.