This is as nearly as tragic as anything I can recall.
Beyond sorrow for the victims and anger for the culprit, my reaction - which is likely somewhat irrational, considering I have children - is that all schools must immediately be operated as secure facilities: locked, metal detectors, and staffed full-time with armed security personnel. I realize the nearly astronomical costs of converting every school into a fortified structure, but, I would ask, can we afford not to?