There has been many changes throughout the years including violence in the schools. Back in the 1950's-1960's, when the "Greatest Generations" kids, in the post war boon that our Nation were being educated there was a sense of morality taught and yes religion in the classroom at least in the sense that there was teaching of Biblical principals and continent . I'm not talking about church indoctrination but rather teaching that human life has a significance to it and was a created thing, by a supreme deity/creator. Since that time evolution has supplanted and eliminated the teaching that included creation. Now I'm not saying to stop teaching evolution but things have turned 180 degrees around and whereas creation was dogma and taught 100% of the time at the elimination of evolution today evolution is taught 100% of the time and creation as well as anything to do with morality is taboo.
I know that the "next step in the parade" is asking "well how would you feel about your kids being taught Islam? Thing is that there are common moral principals behind most all religious teaching and that is that mankind is something special and that life, itself, is something special and to be treasured above other life. Today we teach and lead people to believe that we are no more special than a cockroach scurrying across the floor or some tree planted outside in the yard for it's all life evolved from one organism or molecule. I'm not trying to get in a discussion about evolution but rather to say we are instilling into our children and kids that life has no special significance so why should we be surprised when someone considerers shooting up a bunch of people as justified?
That's not what's wrong with our educational system but I do believe that things like that accumulate into a group that has over the years led us down a path that has brought us to today. I do agree that Teacher's Unions have been a horrible thing along with removing competition from education. Competition works and has made America great and competitive in the world and it could also work in education, I believe. One thing is sadly apparent from the accumulated data over the years and that is that Asian students (China and Japan etc) have excelled in math and science fields and we, in American, have declined greatly. Another area I sadly believe we have declined, over the years, in is teaching about our own greatness. The exceptionalism of American and the system of Capitalism. We are teaching far too many leftist ideology teachings while glorifying socialism and Communism to the point that you would think Communism won the cold war and took over the world. Civics has become a forethought and sideline for students and we are graduating far more students that know little to nothing about our nation's history, government, and founding documents and leaders.
There is a long litany of things that many consider wrong and that may contribute to what we see today and the real question is can we identify what's wrong and turn it around in time to keep from losing another generation? Starting way back we were graduating generations of students ill equipped to compete on a world stage and against other nation's kids. Far too long we have even concentrated ourselves on other nation's kids and concerns over that of our own nation(s). Sorry for opening up such a varied and sticky can of worms.