This is sort of how it works in the UK. You pay 9% of what you earn over £X for 25 years (with X and other details like interest depending on when you started borrowing).

In theory, this stops when you pay off your loan, but the most recent estimate I know of[0] predicts that 60% of graduates under the current system will never get there, so while it's technically a loan, it feels more like a graduate tax.

[0] http://www.telegraph.co.uk/education/educationnews/10747315/... (2014)