BradyFL partner, Giffords, published a compendium of every instance where a firearm has been mishandled in American schools. The current list begins in 2014 and continues through October 1, 2019; they've committed to regular updates.
Leaving a loaded gun out where a student finds it, having a firearm fall to the floor unexpectedly, guns stolen by students from teachers. This list betrays the faulty logic that guns in schools are make our students safer.