If you have a student visa pasted into your passport then you don't need the round-trip ticket. Those who are entering with a tourist visa need to have a ticket leaving Spain.
Almost no one is in class 20 hours a week... When I first got my student visa the paperwork said 16 hours a week. Ever since then, I've studied around 12-16 hours a week. As long as the papers state that you have been accepted and are matriculated as a full-time student studying for a degree, you shouldn't have any problems.
Posts: 1070 | Location: Madrid | Registered: 10 December 2002