LEIGH ROBINSON WAS out for a lunchtime walk one brisk day during the spring of 2013 when a call came from the principal at her school. Will, a third-grader with a history of acting up in class, was flipping out on the playground. He’d taken off his belt and was flailing it around and grunting. The recess staff was worried he might hurt someone. Robinson, who was Will’s educational aide, raced back to the schoolyard.