Social classes are NEVER ACCEPTABLE.
OK, now that I got the political correctness out of my system I should say that this is certainly a tough one. My best g.f. in the entire world came from a home similar, not exactly but similar, to what you describe and they were the greatest people in the world. My parents never had an issue with my staying over at either of her parent's homes or with her being at our house a lot. They treated me like one of their own (they still do). We both came from little money, though, so there wasn't a social class stretch.
I echo Lylah on this one.