Your link shows ~600 people injured or killed in school shootings, across every possible education level (from kindergarten to college) in the course of 24 years. (Both injured and killed, the number actually killed is more like a quarter to a third of that).
That's an average of 25 people killed or injured per year.
ANY school shooting, whether people are shot or injured or killed, or whether the shooter simply misses and nobody is struck, is extremely rare in the United States.
That is to say, it almost never happens.
The few incidents that do happen garner outsized media attention because they are unquestionably tragic. That repeated messaging makes them feel more common than they actually are.
For comparison, fatal car crashes on the way to or from school are FAR more common than school shootings (while still rare.)
Your link shows ~600 people injured or killed in school shootings, across every possible education level (from kindergarten to college) in the course of 24 years. (Both injured and killed, the number actually killed is more like a quarter to a third of that).
That's an average of 25 people killed or injured per year.
Taking enrollment numbers from 2021 (https://www.census.gov/content/dam/Census/library/publicatio...) , it shows that in a given year, ~80 million people are enrolled in those same school levels.
That puts the odd of being injured or killed in a school shooting (if you're currently in school) at 1 in 3,200,000 per year.
So yes, odds of one in three million of your child being involved is "almost never happens".