Why are security systems less effective in public schools than in banks? Because the education system culture is in denial, and we have perhaps entered a new stage of danger. (As a kid, my family never locked our house, nor did any of our neighbors).
Schools are behind the curve, but it isn't too late to correct. My job includes the protection of several adults and children in foreign countries and right here in the U.S.
Their private schools have armed guards, not because they care more for their children, but rather because the reality of threat has been visited upon them and they have accepted the reality, uncomfortable as it is to think about. This not rocket surgery, it's an admission of unmanageability, and a decision to correct the problem by using proven methods.

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Halfway and one more step