How many times per year does a gun go off in an American school? We should know. But we don't.

This spring the U.S. Education Department reported that in the 2015-2016 school year, "nearly 240 schools ... reported at least 1 incident involving a school-related shooting." The number is far higher than most other estimates.

But NPR reached out to every one of those schools repeatedly over the course of three months and found that more than two-thirds of these reported incidents never happened. Child Trends, a nonpartisan nonprofit research organization, assisted NPR in analyzing data from the government's Civil Rights Data Collection.

We were able to confirm just 11 reported incidents, either directly with schools or through media reports.