As I've written several times before, kids used to bring their guns to school all the time. Most schools in the 40's and 50's - and many schools all the way until the 70's, had gun clubs. Kids brought their weapons to school on the bus, placed them in lockers, and went to the range after school. There were virtually no shootings.
With a few, now-rare, exceptions, the practice of school-sponsored gun clubs ended in the 80's. There are examples out there of places where it still exists, but you have to look pretty hard to find them. Guns are forbidden in 99% of America's schools, and yet the number of mass shootings still seems to be climbing.