One of the biggest flaws of "zero tolerance" policies is that they are eminently abusable.
Have an enemy in your class, no problem. Bring a few .22 bullets to school, hang around until after hours when the halls are mostly empty (helps if you have a valid activity to participate in), then slide the bullets through the vent cracks in the other kids locker while nobody else is in the hall. The next morning make sure to be standing by when the kid opens his locker. When the bullets tumble out, or he pulls one out to look at it, scream "He's got bullets, OMG, He's got bullets!!!!!"..... Zero-tolerance = expelled enemy. (Doesn't work if the school has good camera coverage, but there are still ways to sneak bullets into the kids bag, or other property where you can't be seen on camera).