[fleetwoodsnack]

This is a principles based analysis. Pretty common in public policy.

Principle 1: Children should not be victims of arbitrary violence

Principle 2: Children should be educated

These are compatible principles. Your proposal (one of many potential proposals) is to undermine principle two rather than addressing the source of the issue which is violent third parties.

And to forestall any further swiss-cheese a priori logic: this is not something fantastical. There are other societies with have honored both principles one and two, and have experienced zero, as in ABSOLUTELY zero acts of mass violence in educational settings.