As the north side of Chicago has gentrified, many Chicago schools' test scores have improved- evidence that if a city neighborhood attracts enough affluent families, its schools will become more attractive as well.
Poor neighborhoods tend to be fatter than rich ones, whether they are urban or suburban. However, poor urban areas tend to be thinner than poor suburban areas, and rich urban areas tend to be thinner than rich suburban areas.
Some media commentary suggests that fast-gentrifying cities such as Washington are unable to attract families. In Washington, the reality is more complex; the city's high-income neighborhoods actually gained children over the past decade.