I used to be pretty annoyed about school in general, but once I realised how much free time I really have, it's amazing how much I started getting done in that same time.
(As for the actually interesting or difficult classes, which sometimes do exist, you can do the same thing; for instance, in the first few months of my calculus class, I bought a textbook and finished learning the material until the end of the year. Now that class is just as relaxing and as much of a breeze as any other.)