the hard thing about having a kid in school that isn't doing well, regardless of how smart or dumb they are, or how unfair the teachers are, or whatever, is this: you end up spending a lot of time being the bad guy. taking away fun toys, cutting off access the internet/tv/video games, having serious talks basically to yourself because no way is a teenager going to talk to you about what is bothering them, and conferring with your partner about "what should be done." it is such a fucking drag. it's like the terrible parts of being in school with none of the fun note passing and gossiping in the bathrooms.
i distinctly remember being a difficult student, and not understanding why my parents were so frustrated and irate. they were my grades, what's the big whoop? which is why when your parents give you that smirk and say, "just wait," you'll recall it later and think, "well, shit." because they were right.