The biggest recent argument about charter schools boils down to this: Is it okay to suspend a 5-year-old from school? What about suspending him 10 or 11 times in a single year? What about making a list of the students you want to push out of your school?

These are the latest controversies boiling around Success Academy, a very successful chain of New York charter schools that are also a lightning rod for political fights. Two recent media reports honed in on the charter schools' strict discipline policies, arguing that the schools succeed in part because of whom they kick out.

This is partly a proxy war in New York politics, because Success Academy's founder, Eva Moskowitz, is an outspoken opponent of Mayor Bill de Blasio's education policies. It's also the latest manifestation of a broader argument about whether charter schools work because of the kids they educate or because of the way they teach. Whether you see Success Academy as an inhumane test-prep factory or an educational godsend for disadvantaged kids is probably a good indication of how you see the charter school movement as a whole.

Beneath the storm of controversy, there's arguably a quiet point of agreement. Charter critics say the results at places like Success Academy are driven by compositional effects — it's easy to have great test scores if you kick out the worst-performing kids. Charter proponents say that's not backed up empirically, and the bulk of the evidence says they're right.

But Moskowitz defends her school's harsh discipline by saying it's integral to the success of the kids who don't get kicked out. This means that even though Success Academy's great test scores probably aren't a direct result of its suspension policy, its record really is partly due to something traditional public schools can't imitate.

Success Academy is a very successful charter school chain — and it kicks out a lot of kids

Students at Success Academy schools do incredibly well on standardized tests, particularly compared with students in New York City schools as a whole. The charter school chain enrolls 11,000 students, most of them black or Hispanic and poor, in 34 schools across the city.

This year, 93 percent of Success Academy students tested as proficient in math in 2015, compared with just 35 percent of kids in New York as a whole; 68 percent tested as proficient in reading, compared with 30 percent citywide.

Even among urban charter networks, those are outstanding results.

"This is not 'remarkable,'" Robert Pondiscio, vice president for external affairs at the conservative Thomas B. Fordham Institute, wrote when Success Academy's 2014 test results came out. "This is Secretariat winning the Belmont by thirty-one lengths. It’s Michael Jordan dropping sixty-three points on the Celtics in the playoffs. It’s Tiger Woods demolishing the field and winning the Masters by eighteen strokes."

Admirers point to a strong curriculum and intense teacher training. Critics argue that the schools are narrowly focused on test preparation, including rewards for students who score well on practice tests and a combination of detention and study hall for those who do not.

Lately, though, media reports have focused on whether Success Academy students perform well because the school gets rid of kids who aren't going to succeed.

At least one Success Academy maintained a "got to go" list

The most damning evidence was published in the New York Times on Friday. The Times reported on a list of 16 students at a Success Academy school in Fort Greene, Brooklyn. The list had "Got to Go" written on it. Nine of the students on the list ended up withdrawing, and their parents told the Times it was in part due to suspensions, early dismissals, and other punishments that made their lives a hassle.

Moskowitz said in a press conference Friday that the list was an anomaly, the fault of the school's principal, and that it only existed for about three days.

PBS's NewsHour, meanwhile, reported that Success Academy's Upper West Side school suspended kindergartners and first-graders 44 times in one year; one of them was suspended 12 times.

Only one parent would speak on camera, though, and although she and her son were both interviewed about his experience being suspended multiple times from Success Academy, she didn't share her son's disciplinary records with the program. Moskowitz, in a written response, published a long list of the student's disciplinary infractions, which included punching and choking teachers and throwing another student into a wall.

Some observers, including Slate's Michelle Goldberg, have questioned whether releasing a specific student's disciplinary record, usually protected information, is either legal or ethical. Moskowitz argues that it was.

The implication of both stories was that Success Academy's critics are right: The schools are far too harsh, particularly with young students, and their high test scores are in part a result of driving away students who are more trouble in the classroom.

Why Success Academy is at the center of a political fight

Success Academy isn't a random target. It's singled out not just for its standout test scores, but because Moskowitz is a leading opponent of New York City Mayor Bill de Blasio on education policy and is, in some ways, the face of the city's charter school movement.

During his campaign, de Blasio ran against charter schools in general and Moskowitz in particular. New York charter schools can share space with traditional district schools, an unusual practice called "co-location" that can quickly lead to turf battles and conflicts over sharing resources. Success Academy occupied some of the most contentious co-locations in the city, and Moskowitz, a former city council member, had made enemies in the city teachers union before she ever founded her school.

When de Blasio campaigned against co-locations, emphasizing that he wanted to focus on the 94 percent of New York students who do not attend charter schools, he called out Moskowitz by name, repeatedly, as the New York Times recounted in a profile last fall:

"Time for Eva Moskowitz to stop having the run of the place," de Blasio told a United Federation of Teachers crowd in May 2013. Union banners hung behind him as he spoke into the microphone. "She has to stop being tolerated, enabled, supported."

After his election, de Blasio tried to block Success Academy's expansion plans. But Moskowitz proved an adept political operative herself, leading marches in New York and Albany in support of charter schools. New York Gov. Andrew Cuomo supported her, and de Blasio largely backed down.

The controversy means that fights about Success Academy are rarely just about Success Academy. In New York, Moskowitz's prominence means Success Academy stands in for charter schools writ large, and the clashes over its tactics are also about the direction of education policy in New York. Moskowitz is a sufficiently well-known political figure that she held a press conference to say she wasn't going to challenge him in the 2017 mayoral election.

But the fight over charter schools is also bigger than New York — it's part of a broader division within the Democratic Party on education.

Teachers unions and their allies, including de Blasio, generally want less attention and fewer resources for charter schools. Reform-friendly Democrats, such as President Obama, have made encouraging charter school growth a priority. And the criticisms of Success Academy raise issues that apply to the broader charter school movement.

Charter schools suspend students at a high rate

Urban charter schools are better than traditional public schools at increasing students' reading and math scores. They also discipline their students far more frequently — and both critics and some supporters argue this explains why they're more successful.

Charter schools in New York suspended students about three times as frequently as public schools in 2011-'12, the last year for which data is publicly available. The same year, charter schools in DC expelled 72 out of every 10,000 students, according to a Washington Post investigation — 72 times the expulsion rate of traditional public schools. (They've since reduced the rate to 34 out of 10,000, a major decrease, although still greater than the traditional public school system.) In Chicago, charter schools expel students at 13 times the rate of traditional public schools.

The higher suspension and expulsion rates don't count students who leave voluntarily, as some of the students on the "got to go" list at Success Academy did. This forms part of a larger critique of charter schools: They're able to manage their student body so that they have students who are better prepared to learn. More broadly, charter school critics argue that charter enthusiasts make unfair comparisons between charters and traditional public schools when the two systems don't operate on a level playing field.

Expulsions don't account for the charter school edge

The most simplistic criticism you hear of charter schools — that their students' greater success is entirely a product of selection effects or "cream skimming" — has been researched empirically and seems to be clearly false.

It is true, however, that the charter population and the urban district school population differ in a number of ways:

When enrollment is chosen by lottery, students who are attending charters have parents who were involved enough to figure out the process in the first place.

Most urban charter schools enroll a smaller proportion of students with learning disabilities and students learning English than do district schools.

When students leave during the year, not all charter schools let in new students to replace them, even though the schools often have far more students who want to attend than there are spots available. Adding new students, particularly if they're coming from less challenging schools and are academically behind, can be disruptive. But it's something traditional public schools are required to deal with.

But sophisticated studies of high-performing charter schools are able to account for these demographic issues and nonetheless show a charter advantage. A detailed evaluation of KIPP charter schools, another highly regarded urban charter school chain that has faced similar criticisms, found that students changed schools at about the same rate at district schools and charter schools. Students' departures accounted for, at most, one-third of KIPP's advantage on standardized tests. There were clearly other factors at play.

Success Academy has not specifically received as detailed an evaluation, but recall that their students test scores aren't just slightly better than NYC public schools'. Their proficiency rates are more than double what district schools achieve despite an enrolled population that is largely poor and black or Latino. There's simply no way that kicking out 16 "got to go" students could generate effects this large.

The other debate: what to do with student misbehavior

The fight about Success Academy's tactics is also part of a larger debate about school discipline and the right way to deal with students' misbehavior.

The Obama administration, though generally supportive of charters, also wants schools to use suspensions and expulsions less even as many of its favorite charter networks push in the other direction. The administration argues that keeping kids out of school should be a last resort, if it's used at all. They've released data meant to highlight the gap between how black and white students are punished, and pushed schools to use other techniques, such as "restorative justice" programs that bring students together to talk about problems.

At the same time, some charter school leaders — including Moskowitz — argue that tight discipline is key to their success, not by selecting out low-performing students but by creating an environment in which most students can thrive, a point that their supporters echo. While some parents complain that charter schools are too punitive, nearly every article on charter school discipline includes other parents who chose those schools because they wanted an orderly, safe classroom environment.

"Some young children do engage in dangerous behavior," Moskowitz wrote in her response to PBS. "We have a responsibility to ensure that all of our students are safe and learn, and we do this in part by having standards of conduct."

Moskowitz often holds up her schools as a model for what New York public schools should do. And there are plenty of Success Academy practices that other schools could imitate — their curriculum, their longer school day, their high expectations for students and parents. Houston public schools tried imitating practices from charter schools and saw gains in students' math test scores.

But if one secret to Success Academy's high scores is its discipline policy, Moskowitz is acknowledging that she has an advantage traditional public schools don't.

Charter schools can expel students, or suspend them so frequently that their parents decide to send them elsewhere, because district schools exist as a backstop. (An exception — mostly — is New Orleans's all-charter school district, which has dealt with this problem by establishing alternative high schools for students who are expelled. But most of the students have committed serious offenses, and expulsions must go through a hearing.)

That doesn't mean that test scores are high only because low-achieving students are pushed out — the research suggests pretty strongly that they're not. But if your educational advantage comes, in part, from well-disciplined classrooms, and the way you keep those classrooms in order is by frequently suspending disruptive students, it makes it harder to suggest district schools would be more successful if they followed charter schools' lead on everything. It's much more difficult to create a "got to go" list if students have nowhere else to go.