Sgt. Clyde Boatwright, the president of the schools police union, points to school shootings in Parkland, Fla., and Great Mills, Md., as justifications for arming officers. But the Parkland case is no great argument for armed law enforcement in schools — the sheriff’s deputy there at the time of the shooting famously failed to intervene. An armed school resource officer, Blaine Gaskill, acted courageously at Great Mills, confronting the shooter and ultimately firing once at him, hitting him in the hand as he fatally shot himself. But that was a targeted attack on one student, Jaelynn Willey, and it is not clear in retrospect whether any additional lives were saved by the officer’s action.