As president, Bernie Sanders would support a ban on for-profit charter schools and a blanket moratorium on public funding for all new charters, the candidate announced in a speech on Saturday, throwing down a new gauntlet on the left in the Democratic debate over education reform.

The Vermont senator laid out a broad education agenda that seeks to address racial disparities on the 65th anniversary of Brown v. Board of Education. Sanders’s plan is quite ambitious, though it lacks some important details.

He wants to triple federal Title I funding for schools that serve a large number of low-income students, set a national salary floor for teachers of $60,000, and provide universal school meals: breakfast, lunch, and snacks for every student year-round.

But his proposed prohibition on for-profit charter schools and temporary ban on government spending on new nonprofit charters is a foray into the most divisive sector of the education reform debate. Charter schools have been a source of debate for years between mainstream liberals who see charters as a promising alternative to traditional public schools and the labor left that considers them an attack on teachers unions because charters are typically unorganized.

Sanders is firmly in the latter camp and has become the first Democratic candidate to call for a ban on for-profit charters. Other Democrats are much more charter-friendly: Former vice president Joe Biden inherits the pro-charter legacy of the Obama administration, and Sen. Cory Booker (D-NJ) oversaw a major expansion of charter schools as Newark’s mayor.

But with Democratic voters souring on charter schools, Sanders is framing education as another front in his war on corporate interests and these reforms as a tool for racial justice in a broader effort to be more attuned to the interests of black voters in his 2020 campaign.

Bernie Sanders’s big 2020 education plan, explained

Sanders is casting education as a matter of racial equality, releasing it on the Brown anniversary and naming it after the nation’s first black Supreme Court justice Thurgood Marshall, who won the Brown case before joining the court. In that spirit, the senator is embracing the NAACP’s resolution that calls for a moratorium on public funding for new charter schools. He is also demanding a permanent ban on for-profit charters, which serve about 20 percent of the sector’s students.

State and local governments play a far larger role in governing and funding America’s public schools than the federal government does; 90 percent of education dollars come from state and local sources, so it would be a challenge for Sanders, as president, to enact such a sweeping ban.

The US Education Department does spend about $440 million annually to fund the authorization of new charter schools, a money stream that the president could potentially turn off. The federal funding for new charters would be put on hold until a formal audit is completed evaluating how the expansion of charters affects traditional schools. A ban on for-profit charters could require legislation passed by Congress.

For existing charter schools, Sanders would propose that they be subject to the same oversight requirements as regular schools, that half of a charter school’s board members be parents and teachers, and that charters be required to disclose certain student and funding data.

Some education policy experts are skeptical such a blanket policy on charters is a good idea, pointing to evidence charters have improved student performance in certain places.

“Any policy that treats ‘charter schools’ as a single kind of school misunderstands the enormous diversity in the sector. The whole point of enacting a charter school law is to create space for different educational models,” Kevin Carey, vice president for education policy at New America, told Vox via email. “Some have been very successful, some haven’t. Subjecting all of them to a unitary policy, like a moratorium, is a bad idea.”

The rest of Sanders’s education agenda would provide support for desegregation programs, increase funding for magnet schools by $1 billion annually, establish a national per-pupil spending floor, spend more on teacher training (particularly at historically black colleges), and boost teacher pay to a $60,000 starting salary in cooperation with states. He also wants to “rethink” the link between property taxes and school funding, given how such a funding system creates disparities by favoring wealthier neighborhoods.

It’s not immediately clear how actionable all of this is, given the outsized role played by state and local governments in running public schools. But Sanders has laid out a broad set of principles to signal how he would approach education from the White House.

The evolving Democratic politics on charter schools

The other Democrats running for president have been more teacher-focused in their education policy proposals thus far. Sen. Kamala Harris (D-CA) said she wants to provide a historic pay raise for teachers in her first term as president. Sen. Elizabeth Warren (D-MA) has pledged to appoint a public school teacher to run her Education Department. But now Sanders has taken a more absolutist position on charter schools, ramping up the stakes in a policy debate that often goes overlooked in federal campaigns.

Charter schools — which are publicly funded but privately run — swept into the Democratic mainstream in the 1990s.

The idea was that these independently run schools could act as laboratories; freed up from the traditional bureaucracy, they might find new and better and innovative ways to educate students — an idea that won support from teachers unions. Charters, which were still subject to public oversight and standards, were a more palatable alternative to vouchers, which would allow parents to take public money and spend it on private schools (including religious schools and schools not required to take all students).

Democratic-led cities later became the testing grounds for the charter movement; Michelle Rhee, the radical reformer who remade the Washington, DC, school system, became a national star. Disruption was the modus operandi of the day, even in deeply Democratic urban areas, where a generation of malaise had motivated local leaders to think far outside the box to fix their schools.

Barack Obama brought the charter philosophy to the White House. His Education Department used several billion dollars in stimulus money to encourage states to adopt reforms including charter-friendly policies. School officials who crusaded against teachers unions were rewarded with glowing profiles and magazine covers. Against that backdrop, Booker teamed up with the newly elected Gov. Chris Christie, a Republican, in 2010 to make Newark “the charter school capital of the nation.”

Those days were the high water mark of education reform. But the movement’s political standing has been deteriorating ever since.

It wasn’t one blow that knocked the charter movement down. Some of it was the bad aftertaste of vicious reform fights, like the one in Newark. Democrats also saw Republicans across the country trying to undermine organized labor through right-to-work laws, giving them a new appreciation for the public sector unions.

“People on the left see the long-term decline of organized labor in America as one of the single biggest social failures to solve,” Carey says. “So they see themselves in solidarity to teachers unions and opposed to charter schools.”

Isolated anecdotes of charter schools gone bad — like a recent Los Angeles Times investigation revealing one California school that became a cash pipeline for its owners — have added to the perception that charter schools require more oversight.

One newer complication is the Democratic reorientation in the suburbs. Education reform tends to be an issue in poorer urban areas, where schools are at a significant disadvantage and education is seen as critical to upward mobility. But in the suburbs, schools tend to be better performing and better funded thanks to a wealthier tax base.

Thinking about it in raw political terms, “education reform has never had much to say to the suburbs to start with,” Andy Rotherham, who worked on education policy under Bill Clinton, told me. “The suburbs are pretty self-satisfied.”

Mix it all together and charter schools have lost salience in Democratic politics. Education reformers feel like they won the argument, as Rotherham put it, given evidence of improved student performance. But they are also sick of arguing — and they have faded in the center-left policy debate.

Are charter schools good or bad? It’s complicated.

Answering whether or not charter schools “work” is a treacherous task. Assessing student performance is notoriously difficult (and metrics like graduation rates are dismissed out of hand by many academics). Nevertheless, charter school advocates do have some strong evidence in their favor.

The most widely cited (and criticized) research is from the Stanford University Center on Education Outcomes. Their landmark and controversial 2013 report found that students in charter schools saw substantial gains in reading compared to students in traditional public schools. But charter students did not show any meaningful improvement over their peers in math, a decidedly mixed bag.

A follow-up study in 2015 drove home the new consensus on charter schools: They have proven very successful in urban districts and students there perform better in charter schools than in traditional schools on both reading and math. But the evidence is much less compelling in suburban and rural communities.

“The evidence on charter schools is that urban charter schools do a pretty good job for black and Hispanic students,” Rotherham says. “Suburban schools less so. Same for rural.”

As Carey put it to me: “If you have a reasonably large and well-supported charter sector, focused on primarily serving low-income students, it seems to work pretty well. ... If you look at all charter schools, it’s less clear.”

This would track with what happened in Newark, which endured the fiercest fight over charters, but where recent data has been more promising. Even anti-charter officials have not rolled back the expansion for fear of upsetting black parents who like the charter sector, as Vox previously reported.

There are two lines of critique against charter schools. One is that sometimes-mixed evidence of whether they actually improve meaningfully over traditional public schools. The second is that they drain money from other schools.

“This was based on a competitive model and a market theory that is just fundamentally flawed,” Randi Weingarten, president of the American Federation of Teachers, told me of the Newark reforms. “They basically defunded and enfeebled the neighborhood choices that people really wanted.”

The best research on this question probably comes out of Pennsylvania, where Philadelphia-based Research for Action received support from both charter and traditional school authorities to pursue its project. The state had seen substantial charter enrollment growth in the preceding years and the researchers attempted to gauge the resulting impact on the home school districts.

Their conclusion, in one paragraph (emphasis mine):

Using an accounting-based projection model of charter expansion, we estimated a significant, negative fiscal impact of charter expansion in all six participating Pennsylvania school districts in both the short and long term. This is true for districts of all sizes, and does not vary significantly by the rate of charter expansion. Pennsylvania can offset these costs, as it has in the past, by providing districts an additional state funding reimbursement for charter enrollment.

The researchers found that, even though traditional schools have fewer students to educate, they cannot make up for the revenue they lose to charters by closing buildings and laying off staff. They found that the negative effect on traditional schools does diminish — but does not go away entirely — over time. They also noted that the state money can and has made up for the lost revenue for district schools. But that basically amounts to a state bailout to subsidize charter expansion.

This is the core contradiction of the charter debate: There is evidence of school performance, but the concerns about the impact on traditional schools — which still educate the majority of students in most places — have merit.