The New York Times Editorial Board writes that the National Rifle Association and President Obama responded to the Newtown, Conn., shootings by recommending that more police officers be placed in the nation’s schools. But a growing body of research suggests that, contrary to popular wisdom, a larger police presence in schools generally does little to improve safety. It can also create a repressive environment in which children are arrested or issued summonses for minor misdeeds — like cutting class or talking back — that once would have been dealt with by the principal…