At the Furstenberg conference Andrew Cherlin made a case for studying working class family patterns separately from the middle class and the poor. He doesn't want to use class terms, so instead he treated high school graduates, GED holders, and two-year Associates degree holders as collectively the middle group of his analysis.
Cherlin found that women who live with multiple partners -- whether married or cohabiting -- are more likely to come from this working class/middle education group. College educated women are more likely to marry, and more likely to stay married. Poor women are less likely to live with, and especially unlikely to marry, the men they are connected with, even if they have children with them.
Bad things happen to kids each time someone significant comes or goes from their household. Working class kids are even more likely to suffer these disruptions than poor kids are. This is interesting and not obvious.