Teachers expect certain challenges when they sign on in New York City schools, but contending with knife-wielding assailants is not among them. A teacher in the Bronx was stabbed more than a dozen times by a mugger in an elementary school bathroom last month; another was savagely beaten with a bat after confronting a playground intruder; a third was badly injured by a powerful firecracker thrown into her classroom; a fourth was slugged by a student who objected to being asked to put out his cigarette.
City and school authorities reacted last week with stiff security measures: ID cards for students,...