HARTFORD, Conn. — Taking a harder line on crimes no longer seen as juvenile pranks, state lawmakers around the U.S. are proposing stiffer penalties for people who threaten schools at a time of fears over terrorism and mass shootings. As demonstrated by Tuesday's shutdown of Los Angeles schools, threats can cause large, costly disruptions and traumatize students even in cases that might involve hoaxes. While most states already have laws that allow prosecution of a school threat as a felony, there have been proposals across the U.S. to increase punishments, said Michael Dorn, executive director of the school safety nonprofit group Safe Havens International.