On December 14th, I helped chaperone my daughter’s second-grade-class field trip to a local production of “The Nutcracker,” where I spent most of my time not watching the ballet but marvelling at the calm efforts of the teacher to keep the yelling, excited class quieted down. Teaching was not, I concluded at one point, a profession in which I could survive for even one day. Our buses came back to the school at midafternoon, and I and the other volunteer parents left our children for another hour of wind-down time (for us, not them) before returning for the regular 3-P.M. pickup. I came home, however, not to any wind-down but to the unfolding coverage of the Newtown shooting."Cover Story: 'Threshold'"