Each year, parents responding to the Phi Delta Kappan poll report high levels of satisfaction with their kids’ education. Asked to assign letter grades to their children’s schools, the vast majority of parents—generally around 70 percent—issue As and Bs. If those ratings were compiled the way a student’s grade point average is calculated, the public schools would collectively get a B.

When asked to rate the nation’s schools, however, respondents are far less sanguine. Reflecting on public schools in general, a similar share of respondents—roughly 70 percent—confer a C or D. Again calculated as a GPA, America’s schools get a C or C-.

So which is it? Are public schools generally meeting Americans’ expectations? Or are they teetering on the brink of failure?

This may seem like an academic exercise. After all, school quality is what it is, regardless of perception. But, as it turns out, this gap in perceptions is a matter of tremendous importance.

Consider the impact on policy. If the nation’s schools are generally doing well, it doesn’t make much sense to disrupt them. But if they are in a state of decline, disruption takes on an entirely new meaning. Seizing on the presumed failures of the education system, reform advocates have pushed hard for contentious policies—expansion of charter schools, for instance, or the use of value-added measures of teacher effectiveness—that might have less traction in a more positive policy climate.

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.

What evidence exists to suggest that data is the problem? One piece comes from the Kappan poll. In 2002, the year NCLB was signed into law, 60 percent of respondents gave the nation’s public schools a C or a D grade. Thirteen years later, that figure was up to 69 percent. Yet school performance did not change markedly during that time. In fact, scores on the National Assessment of Educational Progress—a nationally representative assessment of student learning—generally held constant or rose slightly during that period.

A second piece of evidence comes from a study that my research team completed in 2015. In an experiment, we randomly divided a diverse group of participants into two clusters—one had access to the state’s data system, heavily reliant on test scores; the other was given a more comprehensive tool capturing a much wider range of factors. We then asked participants to rate two different schools—their most familiar school, which they were able to select, and another school that they were randomly assigned. When evaluating familiar schools, participants generally issued ratings equivalent to a B, regardless of the data system they had worked with. And when using the state’s data system to evaluate unfamiliar schools, they generally issued much lower ratings—closer to a C average. The perception gap was evident.

But something surprising happened when participants used the more comprehensive data system to evaluate unfamiliar schools: Their ratings improved significantly. Even more surprisingly, the scores they issued to unfamiliar schools almost perfectly matched the scores that had been issued by more familiar raters. The perception gap suddenly closed.

Current data systems, which consist primarily of standardized-test scores, misrepresent school quality. They say more about family income than they do about schools. And they say very little about the many things that good schools do. They indicate nothing, for instance, about how safe students feel, how strong their relationships with teachers are, or how they are developing socially and emotionally. They indicate nothing about what teaching looks like, how varied the curriculum is, or the extent to which parents and community members are involved. It’s impossible to know the quality of a school without knowing these things.

Parents have access to this information about their children’s schools, from first-person experience. It isn’t data, per se, but it is knowledge. And that’s why they rate their own schools highly. Whatever the test scores are, they know the teachers and they’ve roamed the halls. They’ve seen work come home in backpacks, and observed their children’s attitudes toward school. Most importantly, they’ve watched their children develop over time.

But other schools? Most Americans have no idea what’s going on inside, except for what they learn from test-score reports.

This is a solvable problem. Groups like the California Office for Reforming Education have begun to significantly expand how school quality is measured. Another group, the Massachusetts Consortium for Innovative Education Assessment, for which I serve as director of research, has established a new school-quality framework that includes the many things stakeholders in education actually care about. Measuring those elements, while shifting away from standardized tests, we are working to build a new kind of data system—one that captures the things parents and teachers know. We believe that this will help close the perception gap. Equally important, we believe that such efforts might help realize the latent potential of data—to inform parents, empower educators, and guide policymakers.

Are the public schools perfect? Hardly. Anyone invested in a school, even a good one, will have a long list of ways they’d like to see the place improve. Inequity remains a troubling reality. And there are some bad schools out there.

But the perception gap is real. And it is deeply consequential—fostering interventionist policy, stigmatizing schools, and exacerbating segregation. In acting on perception, Americans have done great harm to their public schools. But efforts to more clearly represent reality might undo the damage; it might even make schools stronger.

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