Kamala Harris and Joe Biden have catapulted a long-running debate about “busing” and school integration back into the news.

Harris’ criticism of fellow Democratic presidential candidate Biden for his vigorous opposition to court-ordered desegregation in the 1970s has also sparked fresh debate about whether those efforts were successful.

What do we know? In the most basic sense, they did succeed. School segregation dropped substantially as courts and the federal government put pressure on local districts to integrate. But those efforts also sparked bitter, sometimes racist, resistance that shaped political discourse for decades.

“Busing as a political term … was a failure, because the narrative that came out of it from the media and politicians was almost only negative,” said Matt Delmont, a Dartmouth historian who wrote a book titled “Why Busing Failed.” “It only emphasized the inconvenience to white families and white students.”

A political failure does not necessarily mean an educational failure, though, as Delmont and others have pointed out. Indeed, research has consistently shown that integrated schools offered, and still offer, tangible benefits to students of color.

Since public schools in many places today remain intensely segregated by race and socioeconomic status, this issue is not just a historical one.

“School integration didn’t fail,” Berkeley economist Rucker Johnson, who has conducted some of the most far-reaching research on school integration, recently argued. “The only failure is that we stopped pursuing it and allowed the reign of segregation to return.”

At the same time, there is evidence that desegregation efforts have had some unintended consequences, like the loss of black teachers.

Here’s what research tells us about how these desegregation policies worked.

Research shows that school desegregation — often including “busing” — helped black students in the long run.

To isolate the impact of court-ordered school integration in the 1960s, ‘70s, and ‘80s, Johnson used two strategies. First, he compared students in the same school district right before and after court-ordered integration was put in place. Second, he compared pairs of siblings, when one went to integrated schools but the other didn’t.

His conclusions were similar: integration helped black students academically and into adulthood.

The effects were quite large: going to integrated schools for an additional five years caused high school graduation rates to jump by nearly 15 percentage points and reduced the likelihood of living in poverty by 11 percentage points.

In a follow-up analysis, Johnson found that these benefits extended to the next generation. The children of those who attended integrated schools had higher test scores and were more likely to attend college, too.

Johnson’s work is consistent with other research. Another national paper found that school desegregation efforts in the ‘70s reduced the dropout rate among black students, though the effect was smaller than Johnson’s estimate. A study focusing on Louisiana between 1965 and 1970 found that integration dramatically boosted black students’ chances of graduating high school.

Why did school integration make such a difference? Johnson and others show that black students ended up attending much better resourced schools with smaller class sizes.

“Court-ordered desegregation that led to larger improvements in school quality resulted in more beneficial educational, economic, and health outcomes in adulthood for blacks who grew up in those court-ordered desegregation districts,” Johnson concludes.

More recent research continues to find benefits of integrated schools, though they tend to be somewhat smaller.

One study found that when desegregation orders were lifted between 1991 and 2010 in many districts — essentially the reverse of what Johnson looked at — dropout rates jumped by 3 percentage points among Hispanic students and 1 point among black students.

“If policymakers have an interest in increasing the graduation rate of black and Hispanic youth, one tool in their disposal … is promoting racially integrated schools,” said researcher David Liebowitz.

A separate study of an anonymous city school district found that scrapping race-based integration efforts in the early 2000s reduced college enrollment among black students.

Research on the end of court-ordered busing in Charlotte, North Carolina, showed that this resegregation increased arrest and incarceration rates of black male students. (There was not a clear effect on the academic outcomes of black students, though, likely because the district reallocated extra resources to segregated schools.)

Meanwhile, black and Hispanic students who participated in a Bay Area integration program had higher test scores and college attendance rates, one recent paper found. Integrated magnet middle and high schools in Connecticut, created in response to a 1996 state court ruling, have been found to increase student achievement. And research in Montgomery Country, Maryland showed that low-income students who attended affluent schools did better on state tests as a result.

Researchers have also examined whether academic outcomes are simply worse in more segregated schools (as opposed to looking at specific actions to integrate or segregate schools). Again, nationally and in specific states like Texas, researchers have found that students of color do worse when concentrated in racially and economically segregated schools or residential areas. These studies, though, are more limited in their ability to pin down cause and effect, so should be interpreted cautiously.

Two things to keep in mind about all of this research: None of these studies say that schools that predominantly serve students of color can’t be successful, and integrated schools still often have large gaps between white and non-white students when it comes to test scores and discipline rates.

There’s little evidence that integration hurts white students — and it may also reduce racial bias.

Often, the argument against integration efforts is that white students will get a worse education as a result. Most research finds that’s not the case.

For instance, Johnson’s paper found that integration had no effect on white students’ high school graduation rate or adult earnings. Lifting school desegregation orders also didn’t increase the dropout rate of white students, according to separate research.

The Texas study found that attending a school with a higher share of black students didn’t affect the test scores of white students. And a study of a Metco — an integration program that sends Boston students to school in more affluent suburbs — found that it did not affect the achievement of white students in receiving districts.

One exception: the research on Charlotte did find a link between the resegregation of schools there to higher high school graduation rates and college attendance rates for white students.

There may also be non-academic benefits for white students from attending more racially diverse schools. One recent study found that white students who had more black classmates were more likely to have more interacial friendships as children and romantic relationships as adults. Research in other contexts has found that diversity can reduce racial prejudice and improve critical thinking.

School desegregation has had some negative side effects.

One recent study found that school districts in the South that went from being fully segregated to being fully integrated between 1964 and 1972 cut the number of black teachers by nearly a third. Today, many worry about the scarcity of black teachers, who have been linked to the success of black students in a number of ways.

“Desegregation generated large benefits for many groups,” wrote researcher Owen Thompson. “But such a fundamental reform of a major institution also inevitably comes with disruption and costs. The results of the present study indicate that the costs associated with transitioning to a more equitable educational system were in large part paid by African American teachers.”

Even successful integration programs can create unique challenges. The paper on the Bay Area-busing program found that while it benefitted black and Hispanic students academically, it also increased their likelihood of being arrested for non-violent crimes. That could be due in part to traveling more in predominantly white areas and bias among local police.

Finally, another consequence has been “white flight” in the wake of desegregation. This continues to play out — a recent North Carolina study found that Democratic school board members are more likely to make efforts to integrate schools, which cause some white students to leave the district.

White flight, alongside court rulings limiting integration between different school districts, has made these efforts difficult, particularly in cities where virtually all public school students are low-income and non-white. Recent research has shown that even as cities are becoming more residentially integrated, schools generally aren’t.

“There is this incredibly striking trend,” said CUNY researcher Ryan Coughlan. “It raises all kinds of alarm bells and questions as to what that’s about.”