“Some things you just remember, [and] they stop you in your tracks,” upper school history teacher Karen Haley said. On a couch in her home in Dallas, Texas, Haley, a retired U.S. Army captain, sat...

Halfway through period 5 on Wednesday morning, the deep, solemn sound of a bell broke the normal routine of class. A moment of silence followed, heavy with remembrance, before teachers and students resumed...