“Why treat all the students as suspects?”
Did you fly recently?
Have you ever driven a commercial vehicle through a bridge or tunnel in NYC?
The head in the sand “ameich kulam tzadikim” approach, or as the army calls it “dont ask dont tell”, is the cause for a lot of problems. If there is a zero tolerance policy, then thats how it should be enforced, otherwise modify the policy. “Give them a finger, they take a hand” is quite appropo to high school boys.