I've heard of it, you need to apply for a TFL student card or something, and then when you buy a weekly ticket or whatever to put on your oyster, show your student card to the guy and he'll decrease the price.
OK.. so first get the TFL student card (the one that costs like 5 pound a year, yeah?). Then get a regular oyster card. Then put a student weekly pass on it... and it automatically becomes a student oyster card that gives you 40p bus fares? And it works forever?