But unfortunately your schoolwork isn't private, it is likely considered property of the school. You will encounter this in both academia and any job you acquire basically. Work you do for them, or as a part of an assignment they hand you (schoolwork, research in university or whatever task at a job) is their property, that is something you unfortunately need to accept.

Couple that with performing it on a device that is also not yours, but 100% theirs, they are allowed to do whatever the hell they want with it. Even if you did the work on a private device, they sill still own the work and the results you produce.