Everytown's criteria for inclusion in its count are broad. They include shootings that happen at colleges and universities, as well as at high schools and elementary schools. Accidental discharges — when a gun inadvertently goes off in someone's pocket, for instance — are included as well.
Still, the tally gives some sense of the ubiquity of guns and gun violence, intentional or otherwise, on school campuses across the United States. The San Bernardino school shooting is the second in the past three days: on Friday, a student was accidentally shot at a college in St. Paul, Minn., after another student inadvertently fired a handgun through a dorm room wall.
If confirmed, the San Bernardino shooting would be the first this year in which an individual was shot and killed on school property by another person.
Since 2013, according to Everytown, there have been about 200 of these school shootings in the United States -- about one a week. In recent years, lawmakers in numerous states have been busy making it easier for students to carry guns on college campuses. Nine states have “campus carry” laws on the books.
Supporters say the laws help students defend themselves in the event of a mass shooting or other violent incident. But a recent literature review by researchers at Johns Hopkins University found little evidence that concealed carry laws have any effect on mass shooting trends. In fact, they found, the "best available evaluations of these policies indicate that these right-to-carry laws increase violence."