What country are you from originally anitram? You definitely have a point. I think in some cases it's not even personally experiencing poverty...like, for example, a lot of Asian immigrants have been very, very successful in a very short amount of time. I have Asian friends whose parents lived in public restrooms in China, yet by the time they were born in this country, they were richer than my family. But in general they tend to do really well in school because their parents drill the appreciation thing into their head, and because culturally there are such different expectations.
As far as the question about how involved parents need to be with high school students...it's always an added bonus to have parents that support you and encourage you, but at this point I think you really have to do it for yourself. A lot of kids really don't care, and a bunch more know they can scrape by without much effort and still get into a decent college and do fine in life (not a bad idea, sometimes I think I'm an idiot for being such an overachiever in f'ing high school! Maybe with the future of outsourcing it'll pay off.)
Personally, my dad read with me some when I was little, but for whatever reason it always came easily to me and I would do it on my own. I was just the type that could read chapter books before kindergarden, although my dad did make me feel really good about myself so that probably encouraged me. But my parents stopped telling me to do my homework in second grade (because I liked my homework in second grade and did it anyway! haha). One thing that my dad did that really helped me was to debate politics with me and make me feel like he took my opinion seriously, and most importantly helped me consider more than one angle. At age 10, I was sure Bush was evil, this was right before the 2000 elections. So my dad, who hasn't voted Republican since 1980, debated with me and literally reduced me to tears because he took Bush's "side" and made such a good case that I couldn't argue with a lot of his points.
I guess in that way my parents (well, my dad) have encouraged me to some extent. Although at the same time, in the last five years my parents have divorced/split up a few times, we've moved like 5 times (within the area), they've gone through a zillion jobs, a few overly expensive stays at rehab, lost the house, custody affidavits, the whole deal. I'm NOT saying that all situations are the same or that everyone that has some degree of a rough home life should just "suck it up." But it's not impossible to have less than a satisfactory family situation and still take it upon yourself to succeed. I guess my point is that ultimately high school students have to want to do well.
Also someone mentioned that there's not enough retention of skills and that we ought to have more review. Sorry, but are you kidding me?! Yeah, the logarithms can clog my brain to the point of forgetting how to divide occasionally...but SO much of the cirriculum every year is stuff we've been learning since the 3rd grade. I wish I had some stats/links, but I saw some report that compared the percentage of review vs new material (in the maths and sciences specifically) in the US compared to several Asian countries. It was a pretty significant gap. Sometimes I wonder if we'd do better if we were just challenged more and forced to care in order to pass.
I doubt this post makes any sense at this point, but I think it's some sort of mixture of students that really don't care (and see no reason to), and a school system that allows them to slide through with that attitude.