In the US, most if not all states have some kind of law(s) in place that prohibit the carrying of knives in school zones. While most states define a knife as a weapon by edge length, I can not find any legal definition of what constitutes an edge or what constitutes a knife as a weapon in regards to school zones.
Many things that some people may call a knife are not weapons at all such as palette knives, butter knives, oyster knives, etc. Palette knives are even required school supplies for many schools that have an art program.
Then there are things that look like knives, like nail files, letter openers, etc., which are not called knives, have no cutting edge, but which I've heard of people getting in trouble for purely on the grounds that they "look like knives".
There are also many tools that have an edge sharp enough to potentially cut or stab but not things that people would call a knife, like keys, chisels, box openers, saws, screwdrivers, etc. Many of these tools are allowed on school property by maintenance personnel and are required class materials in certain courses like wood-working, and keys are literally carried by everyone who drives into or through a school zone.
Then there are also "blunted weapons". "Wall-hangers" are decorative swords, daggers, etc. that look like they could be real weapons, but are blunted for safety, and so have no effective cutting or stabbing edges. Similarly, a fencing rapier also looks like a full length sword, but has been blunted and is required equipment on school campuses that have fencing teams.
On top of all of this, a handful of states, such as Louisiana, don't even have edge length restrictions that differentiate a short-bladed "tool" from a long bladed "weapon".
So the question is: with all the ambiguity and exceptions, are there any rulings in place that would allow a reasonable person of at least average intelligence to determine what constitutes the crime, and if not, could knife restrictions in school zones be considered void for vagueness under the 14th Amendment?