I can't comment on why I haven't seen them. Maybe I didn't find them.
You're asking other questions.
Most adult psychiatric disorders have their origins in childhood or in adolescence: about 70% or 80%, excluding dementias. Mental health programs in schools used to be a big feature of mental health services. They disappeared for a long time. They're now reappearing. Certainly, Alberta has put a substantial amount of money into developing mental health programs in schools.
Not all schools need the same level of mental health program. There are some real problem schools and problem populations going to those schools who need far more intervention than some of the others. So it shouldn't be that every school should have a cookie-cutter program, but I do think this is very useful. School mental health, for detection, is a very useful mechanism.
Whether you can actually prevent adult disorders, I don't know. Remember that the child guidance movement started in 1928. It was set up on the premise that if you only treated the children you'd have no adult mental disorders. It hasn't quite worked out like that.