America doesn`t have as much social class mobility as we might think. People who do well now generally have kids who do pretty well. There are a lot of reasons for this, but one that`s kind of obscure is the increasing complexity of the meritocratic ladder, often justified in the name of Rights. The result is that kids with smart, hard-working, married parents can get an edge on the system in multiple ways.
For example, when I was a kid, taking the SAT was pretty simple. For example, you didn`t have any right to look at your test once you turned it in. But, now, you have the "right"
to order (for a non-nominal although not extortionate sum) from College Board your SAT test booklet along with a reproduction of your answer sheet (at least for certain test dates) so that you can study what you messed up on. I just spent two hours looking at my son`s May test performance looking for patterns in his mistakes so he can do better on his next try. It`s an intellectually challenging process.
I suspect there are a lot of little angles like that that have emerged in recent decades that help upper middle class families stay ahead of broken lower middle class families.