The Onion

It's only about one per week, if you average it out over the whole year, including when there is no school.
2022 had 51: https://www.edweek.org/leadership/school-shootings-this-year-how-many-and-where/2022/01

If you are just talking about "mass shooting" events, it's closer to 2 events per day in the USA.
https://en.wikipedia.org/wiki/List_of_mass_shootings_in_the_United_States_in_2023#List

There is a mass shooting everyday (on average), school shootings are a bit less often.

There are (on average) around two mass shootings per day, but only (ugh) about one school shooting per week when you actually average it across the whole year. For instance, 2022 had 51 school shootings, but had 647 mass shootings total.

The high number of mass shootings is because anything over 2 victims is considered a mass shooting. So when an abusive dad drunkenly shoots his wife and kids before committing suicide, it’s considered a mass shooting. Drive by gang shootings are frequently considered mass shootings if more than two people are hit. It’s not just an active shooter firing into a crowd, (though those definitely qualify.)

How come there were none last week? Eh? Eh? Can't answer me that one! Trick question! Everyone was out on vacation! But we did have one day without a shooting, the first day. I can't imagine a situation where it takes two days to get someone angry enough to plan something like this though. It's so sad and stupid that we let things like this happen.