I've never even been for my student I.D. at Square One! If you're not a mature student who is obviously older, they just figure you're being honest and sell you the pass without questions.
I had coop in Toronto over the summer and it's a different story at Union, they will not sell you the student pass without GO student ID, even your Mac student card won't suffice. I was too lazy to get a GO student ID made so I solved the problem by buying my passes from Square One instead