I ordered my 18+ Oyster Card, but only realised now that the 30% discount does not affect trains, underground or overground fares (correct me if I'm wrong!).
I am curious about something though. To go to my Uni from home I need to get a train to London Bridge Station, and then a tube from the London Bridge Underground Station. Because you have to tap out when you get off the train and tap back in to get the tube downstairs, does that mean you pay extra?
This is how Oxbridge students do it.