For many in the opportunity-not-inequality camp, the relationship between the two concepts is an inconvenient truth. Concerns about inequality smack of “class warfare,” of “going after” the top 1 percent and Wall Street. Cowen is revealing in this regard: “The inequality focus tends to draw us to redistribution, whereas a mobility focus is more conducive to ideas for wealth creation.”

Many politicians and analysts would rather not address the power imbalances that have channeled so much of our economic growth to the highest-income families. They are much more comfortable focusing on the benign-sounding theme of “wealth creation” or insisting that economic growth alone can improve mobility without any redistribution of resources or political power, as if “a rising tide can lift all boats” matters when a few people are in yachts and many are stuck in dinghies.

But a growing body of research shows strong links among inequality, poverty, and opportunity. For example, new research by Elise Gould of the Economic Policy Institute reveals that of the factors most commonly cited as driving poverty in America—education, family structure, race and more (see chart below)—the number-one factor by far is the growth in inequality, which added seven percentage points to the poverty rate since the late 1970s.

So why is that? How is it that inequality reduces mobility and deepens poverty?

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The relationship between childhood family income and life outcomes is well-established. Socioeconomic status is unfortunately the strongest predictor of a child’s academic achievement, as decades of social science research have found. A child’s income rank—her family’s income relative to the household income of other families—makes a difference for that child’s future adult-income rank as well. Research by Raj Chetty of Harvard and his colleagues links every 10-percentile-point gain in childhood income rank with a 3.4-percentile-point gain in income rank as an adult. Since inequality by definition means that less income will reach poor and middle class Americans for any given rate of economic growth, these facts alone highlight inequality’s relevance to mobility discussions.

In addition, a large and growing body of evidence, recently reviewed by Katharine Bradbury and Robert Triest of the Federal Reserve Bank of Boston, directly connects inequality of outcomes to inequality of opportunity. As shown in the figure below, Bradbury and Triest find a significant, negative relationship between living in an area with greater income inequality and children’s expected upward mobility.

The Relationship Between Inequality and Mobility

It’s critical to understand the fundamental difference between these findings and the Cowen, Rubio, et al. view that America can address poverty without addressing inequality. As just noted, rising inequality implies that the income and wealth generated by GDP and productivity growth increasingly flow to those at the very top of the scale. As a result, relatively fewer resources reach everyone else. One thus would expect to see low-income families less able (relative to the wealthy ones) to invest in children’s futures, more indebted if they tried to go to college, more likely to be stuck in neighborhoods that lack opportunity, and more likely to experience the stressors that do permanent damage to children’s later educational and earnings outcomes.