Anecdotal data from the grad programs in my area is that at least for PhD students your supervisor pays their tuition from whatever funding source they use to pay the stipend.
Yes, and the supervisor also pays a fraction (often 50%+!) of any incoming grant money to “overhead” — to the institution, for lab space, staff, operations, etc.
Why some of this money is categorized as “tuition” and other money as “overhead” is at the root of the question I think.
Why some of this money is categorized as “tuition” and other money as “overhead” is at the root of the question I think.