Imagine what the death toll of the bystanders would have been if a school full of armed teens all began shooting as soon as they heard the gunshot? Not to mention all the accidental mishaps that would likely happen during a normal school day, if everyone were carrying a gun.
It is an important point though, very often there is a rush to legislate and people don't think through the consequences - what happens at the other end of the pendulum's swing and how people could take advantage of the new reality.
Want to kill a load of people? No need to bring a gun, just create a "bang" and watch people draw and shoot all the other people who have drawn to shoot.
It's the challenge with all the "arm everyone" solutions - how do people know who they should and shouldn't shoot. If only there were some kind of badge and / or uniform that the people enforcing lawful order could wear to make it clear ...
But back to this incident: think about whether you see it reported and how quickly it vanishes even if you do, because it's not a white kid with a legal weapon. Anything that doesn't fit a narrative is buried. How many black people have to shoot or be shot to make it news-worthy? Seems a tad racist doesn't it?