When people say Americans are dividing along class lines, they usually mean it as a metaphor. But it's also true in a literal sense. When it comes to where we live, the rich, poor, and shrinking middle class have been moving further apart. Cornell University's Kendra Bischoff and Stanford University's Sean Reardon report that in 1970, 65 percent of U.S. families resided in middle-income neighborhoods. By 2009, that number was down to 42 percent. Meanwhile, the fraction of households in very affluent or very poor neighborhoods more than doubled.
Every city or metropolitan area in the U.S. has higher- and lower-income neighborhoods. The extent to which these neighborhoods differ in their average socioeconomic status, however, varies considerably. Moreover, this socioeconomic residential sorting has grown substantially in the last 40 years (Reardon and Bischoff 2011a; Reardon and Bischoff 2011b; Watson 2009); the bulk of that growth occurred in the 1980s and in the 2000s.
We refer to the uneven geographic distribution of families of different income levels within a metropolitan area as “family income segregation” or, more simply, “income segregation.” Our use of the term “segregation” is descriptive; it denotes the extent to which families of different incomes live in different neighborhoods; it does not imply any particular cause of these residential patterns. We focus on the segregation of families by income primarily because children generally live in family households. Segregation is likely more consequential for children than for adults for two reasons. First, most children spend a great deal of time in their neighborhood, making that immediate context particularly salient for them, while adults generally work and socialize in a larger geographic area. Second, for children, income segregation can lead to disparities in crucial public amenities, like schools, parks, libraries, and recreation.