Ever since the wake-up call that was Columbine, schools and law enforcement have developed multiple strategies to prevent attacks. Indeed, the horror of Newtown needs to be seen in a context that's not defined by defeat. Remarkably, more than 120 school assaults have been thwarted in the past ten years. But, while security hardware and physical barriers can play a deterrent role, it's been psychologists - working hand in hand with law enforcement officers - who have come up with the most helpful tools to prevent violent attacks. 

PBS's "The Path to Violence" tells the story of a powerfully effective Secret Service program - the Safe School Initiative - that's helped schools detect problem behavior in advance.