From the 1940s to 1970s, economic growth was shared among the classes ("A rising tide lifts all boats.") Since the mid-1970s, the majority of economic growth in the US has rewarded the top 20% of Americans ("The rich get richer.")
Economists Goldin and Katz attribute this difference almost entirely to educational attainment. For a while (post-WWII), there were many more people going to college, driving up supply of college-educated workers and closing the income gap between college and non-college. However, starting in the 1960s, that gap started to grow again. Historically, US children would have more education than their parents. That has become less true in the past 30 years. If we are to increase equality in this country, we need to make education a priority for ALL children.