A 15 year old Middletown High School student was arrested for carrying 3 large knives in her backpack. She apparently told the school psychologist she wanted to hurt another student, removed the knives from her bookbag for a school administrator, and promptly walked out the school, knife in hand.
Gun, knife, bomb, etc. etc. it doesn't matter. This is exactly how well "weapon-free zones" work in reality. They don't. If she had decided she did want to stab the student she'd had a confrontation with he/she would be dead. If she'd decided to bring a gun and shoot up a classroom kids would be dead.
Only two things stopped her from harming others. Her own intentions and later the use of force by a SRO. Gun / knife control didn't stop her. It doesn't work and never has.