When graduation balloons popped inside a West Virginia high school, a teacher had to reassure students who ducked for cover that the noise did not come from gunfire. Their reaction showed how the world has changed in recent years — even for teachers who never experienced school shootings firsthand. The teacher was Jessica Salfia, whose mother is also a West Virginia teacher and found herself staring down a student with a gun in her own classroom seven years ago. She was hailed for her role in helping bring the incident to a peaceful end. Already asked to be guidance counselors, social workers and surrogate parents, teachers are sometimes called on to be protectors, too.