The US educational system is very much prestige-driven. It matters more where you got your degree from than what you actually learned, and grade inflation means that grade avarages are pretty meaningless: any good student will average A. The system has several tiers of varying prestige levels: 2-year state community colleges, 4-year state universities, 4-year private liberal arts schools, state research intitutions and private research institutions. People focus on trying to get into Harvard when, in my opinion, they might be better served starting out at a community college (certainly in terms of value for money). However, it seems that most American students are after the connections and the prestige, not the education, and so it matters a whole lot to get into the most prestigious university possible. I think, however, that it is a waste to pay huge tuition and cost of living to be a freshman at a university full of nobel prize winners, because they don't teach freshmen. There is actually an underclass of lecturers with Master's degrees who have two or three part-time teaching jobs at different institutions and are in charge of teaching most of the younger students. Not that they are bad, but they are underpaid and overworked, and class sizes are huge. You are better served at a community college.

If you come from a poor background in the US you can do quite well in the Educational system given enough time. You would start by going to a community college for the first 2 years of your university education, possibly obtaining  an Associate's degree. At more prestigious 4-year, Research or private universities you will pay exorbitant tuition and be in larger classes with instructors who are primarily researchers or not exclusively teachers. At a community college, professional advancement is based entirely on teaching accomplishment, tuition is low and class sizes are small. The only problem is prestige. Community colleges are "where brown kids go to school", and as such they play a key role. It's a shame that they are so underappreciated.

However, if you do well at a community college you should be able to transfer to a 4-year state school and get some financial aid. Since American college students get mostly a general education in their first 2 years, it doesn't really matter that you got that at a community college. Then you can choose any major and graduate from the 4-year school in 2 or 2 1/2 years. Moreover, since these universities don't have graduate programs but the professors are evaluated on research as well as teaching, there are more opportunities for undergraduate research at a 4-year college than at a research university. Some of the best math educators in the US teach at 4-year colleges.

With a good degree from a 4-year state school and some undergraduate research you can get into a public research school for a master's degree with a scholarship or a teaching/research assistantship. Professors at these research intitutions are focused mostly on research and can be of world-class caliber even if the school is not very prestigious.

Now, with a master's degree from a public research university you can get anywhere: law school, medical school, or a Ph.D. program at UCLA or Berkeley, or the Ivy League.

It is a long and winding road, but it can be traversed. The problem is that, for many from depressed backgrounds, high school education is dismal and their community is so dysfunctional that going to a community college is out of the question. Smart kids from depressed backgrounds will tend to find a way in, though.

guaranteed to evoke a violent reaction from police is to challenge their right to "define the situation." --- David Graeber citing Marc Cooper