So the conclusion I drew from the article is that Middle America is still fluid, but the extremes have ossified more, and therefore policy should be directed at reducing the extremes (e.g. capital gains and taxation which contribute significantly to inequality).

At least five large studies in recent years have found the United States to be less mobile than comparable nations. A project led by Markus Jantti, an economist at a Swedish university, found that 42 percent of American men raised in the bottom fifth of incomes stay there as adults. That shows a level of persistent disadvantage much higher than in Denmark (25 percent) and Britain (30 percent) — a country famous for its class constraints.

Meanwhile, just 8 percent of American men at the bottom rose to the top fifth. That compares with 12 percent of the British and 14 percent of the Danes.

Despite frequent references to the United States as a classless society, about 62 percent of Americans (male and female) raised in the top fifth of incomes stay in the top two-fifths, according to research by the Economic Mobility Project of the Pew Charitable Trusts. Similarly, 65 percent born in the bottom fifth stay in the bottom two-fifths.
While Europe differs from the United States in culture and demographics, a more telling comparison may be with Canada, a neighbor with significant ethnic diversity. Miles Corak, an economist at the University of Ottawa, found that just 16 percent of Canadian men raised in the bottom tenth of incomes stayed there as adults, compared with 22 percent of Americans. Similarly, 26 percent of American men raised at the top tenth stayed there, but just 18 percent of Canadians.
The income compression in rival countries may also make them seem more mobile. Reihan Salam, a writer for The Daily and National Review Online, has calculated that a Danish family can move from the 10th percentile to the 90th percentile with $45,000 of additional earnings, while an American family would need an additional $93,000.

Even by measures of relative mobility, Middle America remains fluid. About 36 percent of Americans raised in the middle fifth move up as adults, while 23 percent stay on the same rung and 41 percent move down, according to Pew research. The “stickiness” appears at the top and bottom, as affluent families transmit their advantages and poor families stay trapped.