Between the Lines
Brad, I am much older than you and grew up with the start of television and all those cartoons with violence...I don't think that can be blamed. Nor owning a gun.
Some people grow up lacking a conscience, those we have to worry about.
But most learn by their environments and what they can get away with. It isn't the schools job, nor societies to teach right and wrong and to keep tabs on a particular child. There are far to many children in each classroom with one teacher, to do that
and outside of school is not a teachers responsibility either.
But it is the parent's responsibility no matter what excuse, whether it is they work, or they are poor, or they are afraid to interfere in the child's life. They should know who the friends are, where the child hangs out and if he misbehaves there should be repercussions, anything less, is not parenting.