Perception also shapes the decisions people make about where to enroll their children. If the quality of public education is generally poor, then parents must compete for a small number of adequate schools—a competition that will be won by those with the greatest access to resources. As research reveals, residential segregation by income has increased in the past 20 years—driven chiefly by families with children seeking home in “good” school districts. If the average public school is of C or C- quality, this is rational behavior. But if most schools are good, segregation is being exacerbated by misperception.

So which picture is right? One way to decide is to consider the knowledge base that structures each set of perceptions. Are Americans more likely to be well-informed about the quality of their own children’s schools or to be well-informed about the quality of all 100,000 public schools in the U.S.? The answer seems self-evident.

The question, then, is why Americans maintain pessimistic views of the nation’s schools, even when their own experiences are largely positive.

One obvious factor is the rise of a national politics of education. Beginning with the launch of Sputnik in 1957, leaders in Washington have argued with increasing regularity that the country’s schools are in crisis. From the National Defense Education Act of 1958 through the Every Student Succeeds Act of 2015, the failing-schools narrative has been quite effective in generating political will for federal involvement in education.

Another factor is the unintended impact of civil-rights advocacy. As part of the broader push for social justice, activists in the 1960s and ‘70s worked to demonstrate the ravages of segregation and unequal funding. But the public has not always been careful to distinguish between inequity and ineptitude. As a consequence, many observers have simply concluded that the public-education system is collapsing, and that their local school is simply an exception to the rule.

The biggest factor shaping the perception divide, however, may be data. For the past 15 years, since the passage of No Child Left Behind, Americans have had access to standardized achievement scores for all public schools. But test scores tend to indicate more about students’ backgrounds than about the schools they attend. As research indicates, out-of-school factors like family and neighborhood account for roughly 60 percent of the variance in student test scores; teachers, by contrast—the largest in-school influence—account for only about 10 percent. And test scores convey little else about the many things parents and other stakeholders care about. Consequently, when those external to a school community turn to test scores for information, they are likely to end up with a picture that is both incomplete and inaccurate.