Robert Samuelson has a
column in the Post on the decline of upward mobility in America.
What's being measured is inflation-adjusted incomes, comparing children and parents. So the percentages of children who exceed their parents income has declined. A Brookings
study tries to parse out which classes and which age cohorts see the change.
A couple of observations strike me: it's (relatively) easy for poor kids to beat their parents; it's hard for rich kids to beat their parents. The child of a welfare mother with no job only has to make it into a lasting job while the child of Warren Buffett or Bill Gates will never beat her parents.
The 1940 cohort has the greatest success, so using it as the baseline for comparison skews the results. People like me profited by the post-war boom, the increase in productivity, which hasn't been matched in later years.
One thing the discussions, particularly Samuelson's, don't approach is a hobbyhorse of mine: in a steady-state economy every person who is upwardly mobile has to be matched by another who is downwardly mobile. That's apparent when, as here, you use inflation-adjusted income as your measure; it's less apparent when you talk about people moving from one level (decile, quartile) to another.
With dollars of income, it's possible for everyone to out earn their parents, provided only that the economy grows enough. (Think of China, where the income measure means everyone is upwardly mobile.)