Two side-by-side stories in Sunday’s New York Times show just how prevalent school shootings are.

One covered the shooting at Sante Fe High School, southeast of Houston. The other was all about students at a Mount Pleasant Community High School in Iowa doing math calculations on how likely it was that they would get shot if a shooter turned up in their school.

It seems that high school students no longer just worry about who they will be going to the prom with, or when they are getting their...