There is video evidence of what took place, as well as thousands of witnesses to each and every school massacre. You are truly insane if you believe that all that was forged.
Even without video evidence, to think they are hoaxes is just ridiculous. Imagine if one of these massacres happened at a school local to you, it's such a major event, your whole town or city would know whether or not it truly happened just by word of mouth from the people affected, not to mention local media.