Neither young adults nor empty-nesters are the demographic that impoverished school-age children are associated with, so those populations moving into the urban core doesn't have a very direct positive impact on the educational outcomes of schools that impoverished children attend.
They might, but it hasn't happened yet. Pittsburgh is a good example of a city that hasn't thrived as much as others, but even Seattle city schools suffer compared to the suburbs. "Live in Seattle until you have kids, then move to Bothell or Bellevue."
