Can you think of some ideas on how we can prevent school shootings?

The only thing I can think of is to have a security system like the airports do. Make everyone put their things through an x-ray type thing and walk through a metal detector. Have guards with guns there at the line. No guns can go inside any school or college. It might take a little more time but it will save lives. Those metal detectors don't cost too much, I'd happily donate money toward having them in the schools where I live.