Prison is probably not the answer for high school kids making threats, but 10 or more days in juvenile detention and a psychiatric evaluation might be a place to start, plus much consultation with parents or guardians and other adults in the kid's life.
And if a kid is found to have actually made some preparations toward carrying out a school shooting, much longer term incarceration would be called for.
Cruz had spent a year in an institution and attended an “alternative school” before being expelled. The Sheriff had made over thirty calls to his home He was “in the program”. The program doesn’t work