Across the country this year, according to media reports, at least 11 shootings have taken place on American high school or college campuses, including the attack in Santa Clarita, Calif., on Thursday. And school officials and law enforcement agencies have responded to dozens more credible threats of attacks.

The shootings have occurred inside gyms and classrooms, in parking lots and hallways, and in the crowd at a high school football game.

The New York Times defined a school shooting as one that occurred on campus, in which students were shot, or the suspected perpetrator was a student, or both.