I haven't dug in, but I've looked into this before and you get very different results depending on how you define "school shooting". Everyone thinks of Sandy Ho

I haven't dug in, but I've looked into this before and you get very different results depending on how you define "school shooting". Everyone thinks of Sandy Hook or Columbine or something like that, but some stats also count "drug dealer shot once at other drug dealer and one of them was standing on the corner of the school parking lot", or (less dubiously, but still not exactly what one thinks when one hears "school shooting") a targeted killing, often of a teacher by another adult (think: bad break-up). Or a suicide with a gun at school (as in Pearl Jam's "Jeremy"). Or one student very specifically targeting one other student with no intent of hurting anyone else (bullying, gang stuff, boyfriend/girlfriend drama gone way too far) All those other things are bad, but stats that include them can be misleading if you've got the wrong idea about what they're counting as a "school shooting".