In every single instance involving mass shootings, the common link is a mentally disturbed individual.
Some of these people might have obtained a firearm legally, while many others did not. And in most cases they broke numerous "gun laws" prior to even pulling the trigger. It is not legal in most states for someone of school age to possess a handgun. And bringing the weapon within so many yards of a school is also against the law in most places. What mentally disturbed individual even cares about gun laws?
The focus of school violence prevention efforts should be on identifying persons with mental and emotional problems and getting them the counseling or medication they need to function and to properly behave. Lacking that, they need to be institutionalized for the protection of other students. Institutions could include various types of Special schools or even mental hospitals.
Expanding on this, society as a whole would benefit if more attention were focussed on mental health issues. Unfortunately, our criminal justice system is largely a revolving door at the court house, and most mental health issues are given only rudimentary lip service.
Money is available and already allocated to public schools for Special Education (which includes programs for emotionally disturbed students). Unfortunately, in many places this money is mismanaged and schools actually go out of their way to deny these programs to students in need of them. Parents of special needs children have to be proactive and fight very hard to get their kids into such programs, and it is always an up hill battle all the way. In the end, it often involves very expensive law suits. Losing only one of these law suits costs the school system enough money to have paid for a dozen counselors or special education teachers.
Sadly lacking is any responsible reporting by the news media on recent mass killings. Before any facts regarding who, how, what, etc. are known, they are already babeling about the need for gun control. How many news programs have actually reported on the shooters and their mental issues?
How many of the kids who marched on Washington would consider calling for a ban on violent video games? How many of them watch violent movies or TV shows which glorify murder and violence? And how about the Movie and TV celebs who make appearances to support gun control? They most certainly would be the last to suggest that Hollywood stop producing violent movies.
Making the debate about "gun control" rather than addressing the true problem of mental illness, is not productive. On one hand, you have people who know how to handle firearms properly, and who have a strong belief in the Constitutional Right to Keep and Bear Arms. On the other hand, you have people who know little or nothing about firearms who think that some kind of gun law or ban is the answer. No gun law has ever been successful in reducing violent crime.
There are, and have always been, anti-gun folks whose agenda it is to disarm the country, and they welcome any opportunity to further their agenda. Their arguments are always the same and they include such words as "common sense", "high capacity magazines", "assault rifles", and lately "gun safety". (Ironic since the NRA has been the leader in promoting gun safety for over a hundred years.) Second Amendment supporters know the tricks and arguments of the anti-gunners and will stand up to them without concession because of the long history of their attacks.