...it wasn't that I wasn't interested in school. Actually the problem was I was interested in school and would just read things I was interested in, regardless of whether it was part of the class or not. I've since develped better study habits.
But that last post about Nick Rowe's suggestion to "read a textbook" reminded me of a time that I actually did read a textbook straight through, like you'd read a book, rather than chapter by chapter throughout a semester. It was my freshman year at William and Mary, and I kind of coasted through my intro to microeconomics class but then became a little worried about the final exam. I don't know if it was the study guide or maybe a worse grade on a midterm than I wanted or what, but I had realized I hadn't really read much of anything for the class that semester - I just went off of what was in the lectures. So two days before the final I sat down and read the Stiglitz microeconomics textbook we were assigned cover to cover.
Aside from doing well on the final, it really gave me an appreciation for the sense in which textbooks are a coherent whole. A lot of students think about textbooks as collections of problems, along with some commentary. They don't appreciate the fact that they really are books. I think in grad school you get more of an appreciation of this - and an understanding of how an author's view of the world can really shape a textbook and give it a certain character. Ask a grad student what they think about a given textbook. In most cases, they'll have a very strong opinion about it and back it up with detailed arguments.