WICHITA FALLS — One year ago, David Thweatt made a decision so controversial and groundbreaking the story about it sped around the world. The superintendent of the isolated Harrold Independent School District, about 30 miles northwest of here, made history last August when he and his school board decided to allow select teachers and staff members at the 110-student school to carry guns on campus — a first for Texas and the nation. For Thweatt and his board, the decision was pure mathematics. The school, which sits in the middle of a prairie, was too far from law enforcement for...