I don’t know how available they were in school, but their production was severely curtailed in the early 80’s. I don’t know if even Bill Cosby can get them now.
They were available at my school, as was anything else, though I don’t remember heroin, back in the day. They used our school as the school in a high school drug episode of some cop show at the time and it was typecasting. Busy, absent parents and $$$. And the narcs on campus looked 30 and loved the high school girls. People being bused in from all over the city, meant lots of drugs from everywhere. Entrepreneur zones in the E building.