It would no doubt have an effect, but availability of firearms is probably the biggest factor. School shootings in my country (where gun ownership is strictly controlled) are almost non-existent, but definitely reported on when they occur — probably more so for the very reason they are so infrequent.

This is probably optimistic - they're a meme, kids don't need to see reporting about new school shootings to get the idea that shooting up your school is the way to go, it's something communities are quite naturally propagating amongst themselves - but it seems super clear that they wouldn't have become a meme in the first place without repeated breathless scandalising reporting.