Once, perhaps unfairly, they fit a Mayberry image. School-based police officers were seen as friendly if a bit over-the-hill, a touch out of shape and counting the days to retirement as they watched children head from the lunchroom to recess. If anything serious happened, they were to lock the building and wait for help.
But the string of mass killings at schools over the past 15 years has changed all that, adding urgent new duties and risks to the job and drawing in younger and often burlier officers. Out of hard experience has come a major rethinking of tactics in a crisis.