But the thing is you can't secure schools the same way you secure airports or courtrooms. It's impossible to have that kind of manpower everywhere all the time. And then shooters would simply move to routes children take to go to school.
By far the easiest solution is making it more difficult to get guns.
I mean, you see almost no school shootings in any other country in the world. They happen, but they are so rare. I couldn't name a school shooting in Europe in recent memory. Maybe there is one, I'm guessing there is. But they're definitely rare.