One thing I just really didn't get when I started at the public school was having trimesters instead of semesters (or just all-year-rounders). I thought it was crazy that I could have French I in the first tri and then not have it again until the third tri. I mean, c'mon, most kid are going to forget everything the second tri anyway.
I still think it's crazy. I have classes that last one tri, some that last two, and an A.P. English class that lasts for the whole year. When I was homeschooled, aside from Latin, I was completely oblivious of semesters and trimesters. I just did all my subjects the whole year.
I can understand the logic behind it: if you have tris, there are more subjects the kids can have per year. My argument against this is that you can't really learn too much history in one tri, or even much in-depth psychology in two. In my psychology class, we've skipped a whole ton of modules/chapters. It makes me feel like I should go back and read through those, because of all the interesting stuff we've had to miss because we only have psych for two tris.
But it does make me feel a lot better about what I did when I was homeschooled. Even if I never completely got through my algebra book in a given year, I now realize it was just about as much as anyone at the public school did in a given year. In my algebra III class, we haven't even done much of the problems in the book. We just focus on one sort of problem with its variations and then take quizzes and tests over it. This tri's almost over and I doubt we will have covered all that's in the big ole' Functions, Statistics and Trigonometry book.
Over all, I just don't think tris give anyone much depth in a subject. I believe high school should be more than just a place to get a taste for all the different subjects. I believe it should be a place where you just fall in love with a subject and are encouraged to study it as much as you possibly can.