I don't have kids (only 19) but even at my high-school, we had plenty of this going around. Anything ranging from attempted suicides off the school roof (for reasons that made no sense to anyone) to stinkbombs to a teacher being fired (for reasons we suspected because he was very odd when around kids) to teachers who had no degree in what they were teaching (had a BSc in psychology yet taught accounting and economics even though the book contradicted her half the time), etc... .

MyBestKids2, regarding the grades, I sometimes really hated focusing on it. It wasn't because they were low, it was the other way around and got on honours roll every year. My school was emphasizing to my parents to skip me grades (only got skipped 1 grade) and put me in higher math levels. The school was so-so and instead my parents put me in this separate Kumon thing, along with school. I ended up doing mathematics at least 2 grades higher than ours and I hated it. Part of the reason was I go to ask my teacher something and she says we'll learn it next year. I tell her I'm in the Kumon thing, I'm doing it now and I wanted some clarification but nothing happened. My parents knew this and so did the teacher but oh well. At least now, I've done courses in 2nd year statistics (didn't need to do 1st year stats), teach myself some abstract algebra, etc... .

Happily, in high-school, I found some smart friends and we went (by that, I mean a hell of a lot of nagging over and over by the math teacher) to enter math competitions with other schools around the province and country. We didn't do amazingly well, I think in the top 5 one year due to an amazingly talented kid but the rest was in the top 10 or below out of 100+ schools.

Try to help her out if you want or try to use something like Kumon or similar tutors. Sometimes it's the method of teaching that she isn't good with. For myself, I'm amazing at memorizing, which makes memorizing pages of human anatomy pretty easy. When it comes to applying it, such as for math, I take a different approach but it works also. For English, well, I'm sort of screwed and get mid to low 70%. For math, memorizing it isn't great and instead I teach it to myself differently and it works. Perhaps try giving her alternate ways to learn.

But try some tutors for your daughter and see if she is working to her max. potential. She may just not care and not try all that hard. When she gets a poor grade, that creates the circle and she becomes sad, knows she's disappointing you but doesn't know what to do. Or it could be she truly doesn't understand the material.