[lz400]

That's not correct. It counts the total number of school shootings. Some of those shootings had no victims. The total of students shot is also provided with some more elaboration with charts here.

https://www.abc.net.au/news/2024-12-17/us-school-shootings-2...

As you can see your number of 13 makes no sense, there were 200-300 students shot (!)