CLARKSVILLE, Ark. -- As Cheyne Dougan rounded the corner at Clarksville High School, he saw three students on the floor moaning and crying. In a split-second, two more ran out of a nearby classroom."He's got a gun," one of them shouted as Dougan approached with his pistol drawn. Inside, he found one student holding another at gunpoint. Dougan aimed and fired three rounds at the gunman.Preparing for such scenarios has become common for police after a school shooting in Connecticut last December left 20 children and six teachers dead. But Dougan is no policeman. He's the assistant principal of this school in Arkansas, and when classes resume in August, he will walk the halls with a 9 mm handgun.