The Oakland school board has a problem: too many schools and too few students. To stay afloat, the district plans to close as many as two dozen schools over the next five years.

That decision has not gone over well with the teachers and students affected.

“I know you think that [it] is a low-quality school, but they produce high-quality students,” one teacher said at the emotional meeting when the board announced the first closure.

Similar scenes have played out across the country. In some cities, the rapid growth of charter schools mean students are spread too thinly across too many district buildings, prompting closures. In other places, a declining number of school-age students is the culprit. And elsewhere, policymakers have been motivated to close schools by a desire to improve academic performance.

In the 2014-15 school year, more than 210,000 students attended a school that would be closed that year, according to the most recent data from the federal government.

So what are the consequences? Overall, do school closures set displaced students on a negative academic trajectory, or do they more often help students escape schools that have long struggled?

At this point, we have some answers. A new study focusing on the effects of 20 school closures in Philadelphia is just the latest in a substantial body of research on what happens when a school is shuttered.

Chalkbeat reviewed 17 studies published over the last decade, which look at how closures affected students’ academic performance in different cities and states. (You can find all the studies here.) They help answer a key question for those who fear closures hurt students academically — though they can’t capture other impacts of school closing on a community.

Here’s what we learned.

1. In many places, closures hurt students academically; in some others, they helped. Nationwide, closures appear to slightly lower test scores.

In a few cases, students whose schools closed benefitted in at least some way. That was true in four studies Chalkbeat reviewed: in Ohio, for instance, students saw major jumps in test scores post-closure; in New Orleans, closures boosted high school graduation rates by about 20 percentage points.

But these results were more exception than rule. In several other places, displaced students were harmed in measurable ways.

In Milwaukee, for instance, high school closures caused steep declines in high school graduation and college enrollment rates. A recent Chicago study — focusing on the highly controversial round of nearly 50 school closures in 2013 — showed that affected students had lower math scores even four years after the closure. (There were no clear effects on suspension or attendance rates.)

In another handful of studies, students’ academic performance declined but eventually bounced back, suggesting the closures were disruptive but the effects were temporary. A Michigan study looking at nearly 250 closures over a few years found a drop in math scores for displaced students after one year, though by year three the negative effect had faded away.

Based on these divergent results, it’s not a surprise that a major national study lands somewhere in between. This 2017 paper looking at over 1,500 closures across 26 states found, on average, very small negative effects in math and reading on displaced students.

2. It really matters the quality of the school displaced students end up moving to.

It seems obvious, even circular: students who move to a higher-performing schools do better. Research has confirmed as much. In eight of nine studies looking at this, there is evidence that students who end up at higher-performing schools are better off than those who switch to less successful schools. That includes the national study.

This can make all the difference: In some cases, students in better schools benefit academically from closures, while students in worse schools are harmed.

The problem is that in many places, displaced students don’t end up in schools that are much  better, which helps explain the mixed results overall for closures.

“We find that closures have the potential to benefit the achievement of displaced students if they transfer to high-performing campuses,” write researchers in a Houston study. “Unfortunately, our analyses of student transfer patterns suggest that few students, particularly low-performing students and students of color, transfer to such high-performing campuses.”

3. In some cases, other students do (slightly) worse when their schools receive an influx of students from closed schools.

The impact on the students at the schools that receive lots of displaced students often doesn’t get a great deal of attention in debates about school closures. But it’s an important issue that at least six studies have examined. Four found that closing schools clearly hurt the academic progress of students whose schools weren’t closed but received new students as a result.

In general, these effects were modest. For example, in the recent Philadelphia study, receipt of new students caused suspension rates of existing students to increase by about 3 percent. In the Chicago study, new students hurt reading scores among students previously enrolled, but that effect disappeared after one year.

4. Researchers know little about how school closures affect future students.

This is a crucial issue, because closing a school also affects students who would have attended that school but now end up elsewhere.

That’s difficult to study, and there appears to be only one paper directly examining this question, focused on a group of New York City students who would have otherwise attended a high school that was closed.

“This shift in [students’] enrollment options led to improvements in students’ attendance, progress toward graduation, and ultimately, their graduation rates,” the researcher wrote. The gains were large: graduation rates jumped 15 percentage points for those students.

The New Orleans study simulated the consequences of closure for future students, and also estimated that the academic impact was positive.

Another way to answer this question is to look at the performance of a city’s newest schools, since closures are often caused by the opening of other schools. Those new schools are frequently charter schools; nationwide, charter and district schools perform comparably, but charters tend to do better in cities.

5. The impact of a school closure on communities and students goes beyond academics, and researchers have documented consequences that aren’t easy to measure.

Even when schools are closed as part of an effort to save money, public debate often focuses on another outcome: the pain caused by shuttering a community institution.

“Institutional mourning is the idea that people mourn institutions the way they also mourn people,” University of Chicago sociologist Eve Ewing told Chalkbeat recently. She coined the phrase after conducting interviews with Chicago residents affected by closure. “The way they used this intensely intimate and emotional language to talk about their own reaction to that perceived death is something that happened over and over,” she said.

School closures may also galvanize political activism. Chicago residents who lived near a closed school were more likely to vote and take political action, and less likely to support Mayor Rahm Emanuel, who controlled the schools, other research has found.

In another study, 40 percent of students reported that the closure of their high school damaged their friendships or other relationships. Others said they were stereotyped at their new schools. “People label us as bad, stupid, or useless but people don’t know what it feels like to be forced out and no one will ever understand the struggles we face every day,” a student said.

Research in Philadelphia found that arguments about hard-to-measure characteristics of a school and the strain of closures on families, were generally not persuasive to the state-run school board.

A final issue is the fact that school closures disproportionately affect low-income students of color. The national study found that even among low-achieving schools, those with more students of color, particularly in the charter sector, were more likely to close.

“It causes political conflict and incurs hidden costs for both districts and local communities, especially low-income communities of color that are differentially affected by school closings,” wrote researchers in a report critical of school closures.