http://www.epi.org/publication/usa-lags-peer-countries-mobility/
I also listened to a podcast by economists that compared people moving from the lowest 20% of income to the upper 20% of income in one generation. To keep it short, the US is somewhere around 7%, Canada is at like 13%, and Denmark is at like 14%. These were the examples I remember.
It should also be noted that the LARGEST percentage possible is 20%.
In addition, a few decades ago 90% of 30-year olds made more money than their parents had earned at that age. Now that number is closer to 50%.