Don't have school-shooting rates but the murder rate in the 1800s in America was a lot higher than it is today.
Last time I checked there were no Tarantino movies or Call of Duty games in 1850.
And the murder rates in the 15th and 16th centuries were much higher than they were in the 17th and 18th centuries - which would indicate that murder rates aren't tied to the lethality of available technology but rather to how civilized people are and how able they are to control their violent impulses.