Most school shootings in America are committed by young people, while adults commit most of such crimes in other countries--and there are fewer shootings in other countries.
My explanation is that very few human beings are capable of going to a school and shooting people. In the U.S., quite a few of these unusual individuals are able to get guns when they are young, and they proceed to commit their once-in-a-lifetime crimes. In other countries, these disturbed individuals can't get the guns until they are older, at which time some of them have calmed down and established peaceful lives.
This topic should be discussed openly at Castle Park Elementary in Chula Vista. A disturbed goup of teachers has been struggling for years with an urban legend started by Robin Donlan and her friends, and exacerbated by Cheryl Cox and her lawyers, that someone is going to come to Castle Park Elementary and shoot everybody.
These cynical educators and education lawyers have compromised the mental health of several teachers at Castle Park, resulting in deep paranoia imposed upon earlier mental problems.
Those responsible should try to undo the harm they have done. One principal and one district administrator tried to fix the school, but they went about it in the wrong way. They didn't shine a light on the truth to benefit the hysterical teachers, they just tried to transfer out those who had kept themselves in power by whipping up the staff into a years-long frenzy of anger and fear. (It's a common strategy: to make people afraid by ranting about evil "others" in order to exert control over and loyalty from frightened people, while at the same time carefully covering up the truth.)
In CVESD, the lawyers and teachers union, Chula Vista Educators, have stood in the way of any help for these troubled teachers. Who suffers most when a teacher is crazy? His/her students do--both academically and psychologically.