I highly recommend this discussion of social class, and classism, in the U.S. It raises the point that, in the times that we do talk about class, we generally use indirect referents such as economic class or education levels, and these really aren't class as such. And, by talking about them, we completely miss the effects that class differences have on us.
If you interview people, read this and think about whether your interview habits are selecting for people of the "appropriate" class, by selecting for people who perform competence in the way that you expect rather than the way a different class might expect.
If you think four-year residential colleges are a complete waste and can be easily replaced by distance learning or online classes, read this for the section on what people get out of college -- and, in particular, what it does for class mobility and why.
And, in general, just read it, because it is pretty critical to understanding the social world we U.S.ians live in, and it's something that we really don't talk about much at all -- it's taboo enough that it's easy to just completely not see it!