Will income inequality cause class warfare? by Ray B. Williams FROM Psychology Today

"The chance that children of the poor or middle class will climb up the income ladder, has not changed significantly over the last three decades." - From a Pew Foundation study.

But please see the graphs and tables from the study Income Mobility and Economic Opportunity by Christopher Frenze for a contrary viewpoint:
http://www.house.gov/jec/middle/mobility/mobility.htm