Proponents of integrating schools socioeconomically, like Kahlenberg, argue that, in the aggregate, families like Alison's will probably benefit the public schools they join. That's because going to school with many children from middle-class families—defined as a family of four with income of $40,000 or more a year—boosts their lower-income peers' academic achievement. Students influence one another, from their aspirations to the ways that they behave in the classroom, he contends, and middle-class children are on average more likely than poor children to be academically engaged. Then there are the parents. Middle-class parents are four times as likely to be members of the PTA as low-income ones, according to Kahlenberg. They're also in a better position to hold school officials accountable and use their cultural capital—from fundraising to lobbying—to advocate for more resources for their child's school and the district. Finally, many teachers perceive working at a middle-class school as a promotion, making it easier for such schools to attract talented staff.
That's not to say a handful of middle-class and wealthier students yield a magical transformation. Kahlenberg thinks the threshold for socioeconomic integration, where middle-class-student achievement doesn't decline and low-income students benefit, is about half and half—50 percent of the students qualify for free or reduced lunch and 50 percent don't. Other experts put the ratio at 60 percent middle-class or higher.
Attitude matters, too. In a recent study, Erin Horvat and Maia Cucchiara of Temple University found that not all parental involvement by wealthier parents in urban public schools is created equal. At one of the two urban schools they studied, Horvat and Cucchiara found that parents strove to improve the school as a whole. At the other, they focused more narrowly on improving their own children's experience. The split made a big difference in the types of improvements the schools saw, who benefited from them, and whether those changes lasted over time. For example, one dad spent a summer wiring the entire school, because he wanted all the students to benefit from computer access. Cucchiara offers this advice: "Don't just raise money or get special programs for your kid's class."
Some children moving out of private schools won't change the profile of the public schools they move into one iota, because their families live in well-off districts or move there to get away from struggling, urban schools.
"We had to move in order to send our son to a good public school," writes Laura, who lives in south-central Pennsylvania. "We moved only two streets away, but that took us out of the worst school district in the county and into the best school district in the county, which is indeed in a suburb."
Private schools, meanwhile, are trying to hold their enrollment together by extending financial aid to more families; the National Association of Independent Schools found in a survey of its member schools that the numbers of students who receive aid has increased from 16 percent to almost 21 percent over the last five years. And yet parents are still scrimping. A mother in the Los Angeles area who lost her job in 2009 writes of how the family pays her son's $28,000 tuition in part by clipping coupons for groceries and driving used cars into the ground. While she explored sending her son to a magnet school in Los Angeles, this mother was put off by large class sizes—30 to 35 and even occasionally 50 students per class—as well as unresponsive administrators and counselors and limited art and foreign language offerings. But because she and her husband are sacrificing to keep their son in private school, "I think we end up putting some stress on our son," she says. "If we find he isn't taking full advantage of programs his school offers that would bolster him in some way, we tend to hit the roof."
For children who stay in private schools, the sudden disappearance of some of their peers raises questions. One mother of three in suburban Philadelphia wrote that friends transferring to public schools had inspired her son to ask for a more in-depth explanation about why he goes to a private one. She found herself searching for words to explain "why it's all right for him to go to this more expensive school that we feel is better, but it's also all right for his good friends, about whom we care so much, to go to the public school which we decided wasn't 'good enough' for him." With more kids discovering that public schools are—or will have to be—"good enough" for them, just think of the other lessons to be learned.