HOW COMMON ARE MASS SHOOTINGS AT U.S. SCHOOLS? Not very. And they don’t appear to be getting any more common, though 24/7 cable news coverage may give that impression. Ilya Somin writes: “The extreme rarity of such incidents should be kept in mind as we decide what, if any, policy changes should be made in response to the Virginia Tech tragedy. Some changes may well be warranted, but we should guard against costly overreactions such as the draconian ‘zero tolerance’ policies implemented in many schools after the Columbine attacks in 1999. As a professor in the Virginia state university system (of which Virginia Tech is a part), I hope we can resist the temptation to enact similar measures.”