I do not know the details of turning it off, but there have been threads in which people didn't have access to the AI functions and they found out that their IT department has turned it off. Those were company accounts. So maybe the school's IT department could get in contact with their Adobe tech person and inquire that.
If it's not possible to do the same in education accounts, then of course you could make a documentation of the creation process a part of the homework. Let them document their process with screenshots and descriptions. It's good for reflecting anyway. And also when they want to remember later on how they did something in that homework, then they can just read their own documentation.
And maybe check out this: https://helpx.adobe.com/enterprise/kb/adobe-firefly-for-k12.html#:~:text=Select%20the%20View%20Details%20icon,user%20assigned%20to%20this%20profile.