Cripes. The best years were either Grades 5, 7 (although it didn't start out all that well), and 9. Grade 5 was great because I had a great teacher (once she returned from materity leave, which meant she didn't show up until November) and good friends. Grade 7 was similar, although I wasn't a fan of my Math teacher (he sounded a lot like Brad Garrett and was really kinda tough). Grade 9 was great, aside from the month of March, which was god-awful annoying and I'm not getting into specifics here.
As for the bad years, Grades 3, possibly 8, 11, and almost all of college apply here.
Grade 3 was bad because I really couldn't focus all that well in class and always seemed to be the only one who couldn't finish their work in class (and thus, had homework.)
Grade 11 was miserable because I just couldn't finish papers on time, I was generally frustrated with no way to express myself, lonely, broke, and just plain depressed. College has really been like Grade 11, over and over again in this regard. Thankfully, I'm done at Seton Hall in May.