support permitting teachers/principles who voluntarily choose to be properly trained in defensive security and be armed

If our society/parents would support permitting teachers/principles who voluntarily choose to be properly trained in defensive security and be armed our schools would have a natural built in improved security system protecting our children. What is the average time it takes for police response verses incidents to take place that cause such tragedy as Newtown? If those present were enabled to be better prepared to defend with deadly force it is highly likely such incidents would greatly diminish or be eliminated. Does the individual who typically takes such cowardous action choose targets that are least likely to be a threat to their action? It seems to be the typical criminal mindset to choose a target of opportunity of least resistance that needs to be countered w a serious deterrent.