For instance, the Washington Post reported that in one case bullies at Columbine twisted a student's skin into bruises and made anti-Semitic slurs. People called him freak, dork, nerd, stuff like that. True, it is possible to overstate the problems with government schools. I quite enjoyed my high school experience, and I recognize that most of the staff at my school were both caring and competent. However, a good staff cannot overcome the institutional problems.
Drug use is rampant at government schools.
Students are forced to interact with others who are violent and mean. Administrators are forced to admit every student, regardless of behavioral problems. At best, students succeed in their classes, fit in socially, and waste a large portion of their time dealing with bureaucracy and the minority of teachers who are incompetent. It's tautological that if the killer had not had a gun, he would not have killed people with a gun. One possibility is simply to reduce the number of potential teen murderers.