Whether it be guns, video games, movies, evil lefties, evil righties or fucking king tut the root of the problem is society and how we have evolved into a group of separate people instead of a family, then a village and then a city and then a state and so on.... we are all in our separate worlds these days. 
there are a few books on the matter of societal influence on youth and the outcomes. 
Iron John is one examining mens issues and the other is Boys Adrift. 
In Iron John it is explained through a critical analysis of a a Grimm Fairy tale. That book holds a lot of truth to me. Mostly from my own life and through leading young men and watching them grow. Men have a need to belong and be accepted. Since our society moved to industry and working in abstract it is harder and harder for the dad to demonstrate that he does something of value. If he is present at all. Role models are almost non-existent in young-men's lives because of the fears driven by everything from pedophilia to corrupt influence. it is saddening and sickening. 
Adrift hits more of a parenting angle with a focus on the psychology of the young male mind but again blames societal change for the problem. he offers decent methods to change course. 
The problem for me is we are losing half our countries most precious assets. There is zero mystery in why most bizarre acts of aggression are perpetrated by young men that are predominantly white. Although for some similar and some different you could argue the black youth has been destroying itself for the last five decades.  
That is kinda what I wanted to discuss, society and its effect on our youth NOT predisposed political postions that have been posted ad nauseum. 
But go forth and prosper I wont change the course of the thread if you all dont want to change.
		
		
	 
As far as schools -- they're no longer the major influence they were twenty years ago, thanks to changes in communications technology.  The system we use was outdated then; it's close to useless now -- seeing as it was developed to produce "productive citizens" for a society where conformity was prized, and the set of skill sets useful in life was far, far narrower.  If any blame can be placed there, it's that teaching facts can't possibly produce responsible people when no critical thinking skills are imparted.  There's a failure in values, too, but really on just one area:  we do not teach self-ownership, which is the foundational truth for mental health, self-responsibility, and respect for others.
But...
There's a serious point above about role models.  In an attempt to "protect" young people, the legal structure of our society has in actuality been building ever stronger fences between responsible adults and young people, especially teens.  There's always been a generational division, but now the law itself turns adults into the enemy, unless they're adults willing to break the law.
One glaring exception is where wealth intervenes, but the know-your-place authoritarian propertarianism espoused here as "conservatism" is as bad as (or worse than) the culture of rebellion, drugs, and alcohol.  That neo-fascist view of the world is at least as destructive to respect for other human beings as anything propagated by street gangs (or held up for admiration by rappers).  
I can't decide what book you have in mind with 
Adrift; more details would help.  But young people are adrift, because it's pretty plain that the one side claiming to represent values really represents a selfish pursuit of wealth and power, while the other side represents a demand for mushy conformity under an authoritarianism poorly disguised as "caring".  The combined lesson is to not give a shit about others, but to grab what power you can, and use others as pawns to get where you want to go.
So the real surprise is not that we get young people who do mass murder, it's that we get as few as we do, and also don't have them blowing things up and burning things down on a serious scale on a regular basis.