As someone's who's been in the school system for years, and is now a senior about to leave it, hopefully I can provide some perspective ( though I probably won't).
In my school, the system is designed to facilitate students through without regard to how well they learn. The only exceptions I can think of are AP classes, because the AP exams are conceptual based, and the school doesn't want to look bad so effort is put into making sure that our AP classes are top notch. AP classes are heavily focused on the conceptual. For my AP Physics class, for example, I don't think I've memorized an equation all year, a it is also the hardest class I have. The lower courses aren't designed to help you learn - they're designed to help you get good grades, without regard to how well you know the material. See, to the school, your learning doesn't actually matter. They just need you to graduate the school system, and go to college, so so they look like a good school system. You just another notch on the belt to the administration. The grades you get in lower levels don't really indicate anything other than effort. I think there's a certain level where to get lower, you'd have to be actively trying to fail.
Another downside is incompetent teachers. Even AP isn't immune to this, though it is more restricted to the English department. In AP Language and Composition this year,I have not learned a thing from my teacher. In Pre Calculus last year, I didn't learn a thing from my teacher. I self taught myself a lot of the concepts.
In the end though, the failures of the school system don't really hurt me all that much. It actually helps a bit. I'm one of the smart ones, so I over perform in comparison to my other classmates.