Being as they of course "just can't" do anything to stop people from bringing guns into schools -- in a way, this makes a certain kind of sense for them.
[1] https://www.mcgruffsafekit.com/ [2] https://www.latimes.com/archives/la-xpm-1990-08-07-me-81-sto... [3] https://www.nytimes.com/1983/02/22/us/fingerprinting-of-chil...
We (students) knew back then who was disturbed, who would likely carry a gun or knife to school, who might pull a weapon in a cafeteria argument. We all did that "sad calculation" you mention.
When it came time for my own kids to go to school we opted out and homeschooled. Not so much out of fear of mass shootings, but because schools are terrible environments for children in so many ways, and it's easy to do better than what passes for "education" in the US.