principia_coh is, of course, more than capable of defending her own points, but I would like to point out that Martha did make the choice in The Lazarus Experiment to be 'more than a passenger' with an undetermined departure time. No, she didn't realize how much time she would lose due to unforeseeable events, but that's really the point -- she decided that she could be away from her studies for an unknown period of time. She made no reference to continuing her studies on the TARDIS (though she did, as you point out, mention that she's a student in FoB) nor did she show any interest in the medicines of the various places and times that the Doctor took her.

By your reasoning, any student on a summer break between semisters or takes a year off for traveling are screwed, right?

Actually, a portion of the first few days/weeks back into a school year does tend to be review-based, for the very reasons that principia_coh stated. People forget things over summer break.