A thermal typewriter will be the quietest option. As a high school teacher with typewriters in my room, here is my experience: kids are allowed to use them during passing time and if we have some independent time and they are done with their work, but they are too noisy to use for notes or during instruction. If a student wanted to use a regular manual typewriter during class, I would ask them to stop, because it would be too much of a distraction to the class (and me).
https://www.reddit.com/r/typewriters/comments/1wvrlad/best_typewriters_for_school/
Advice from a self-identified high school teacher with manual typewriters in their classroom.
