Copy machines were too expensive to use for school work. I remember some machine that used a hand powered roller to spit out copies in a pale, blue ink. This was late 70’s/80’s.
We had two options to create the stencil: there was a special machine that used some kind of electrical process (I don't remember details) to scan a printed sheet and "burn" a stencil from it, so you could copy arbitrary originals; or you could cut the stencil directly on a typewriter (with no ribbon), which gave a sharper result -- but you really didn't want to make too many typing errors, there's only so much you can do with stencil correcting fluid.