The psychology that causes school shootings...
The United States generally has a violent culture. If you removed every shooting of any type (school, mass, crime of passion, etc) from the crime statistics the US would still have a higher rate of violent crime than any other industrialized Western nation.
Aside from that it's time to stop blaming Reagan for the mental health crisis in this country. Aside from the fact that our mental health system was a horror show when Reagan ended it the guy hasn't been President for over three decades. That's plenty of time for individual States and / or the Federal Government to have reversed course.
Plenty of countries with more guns per capita than the U.S. that don’t have school shootings.
There is no country with more firearms per capita than the United States.
Even if you go by household, to reduce the effect of people who have more than one firearm, the U.S. still ahead of any other nation.
To be clear we can and should do more to reduce gun violence in the United States and small things like prosecuting adults who are accessories to shootings are a good thing.
Yes it would. Adults, including parents, are increasingly being charged in other types of shootings such as when one child is playing with a firearm and accidentally shoots someone else. It's not happening often enough yet but it's growing in popularity. If you can remember long enough, I know I won't, check back in a year and lets see what happened. :)