Complex sentence: As a result, the U.S. educational system significantly aids in widening the gap between the rich and the poor, a gap that has increased, rather than decreased, over the past few decades due to lack of social mobility.
Split into simpler sentences: As a result, the U.S. educational system significantly aids in widening the gap between the rich and the poor. This gap has increased, rather than decreased, over the past few decades due, in part, to a lack of social mobility.