ATLANTA (AP) — If you want to know where mass school shootings are most likely to occur, look no farther than small-town and suburban America.

The massacre that killed 10 people at a high school in Texas last week was just the latest to happen in a small or suburban city. Of the 10 deadliest school shootings in the U.S., all but one took place in a town with fewer than 75,000 residents and the vast majority of them were in cities with fewer than 50,000 people.

These are seemingly idyllic places to grow up: low crime rates, good schools and a sense of community where everyone seems to know your...