This viral video of a teacher berating a student is a window on the charter school debate

A secretly recorded video of a teacher at a well-known New York charter school berating a first-grader in front of her classmates for failing to explain a math problem correctly, first published in the New York Times, is getting a lot of attention. And it's easy to see why:

In the video, a teacher at Success Academy Cobble Hill, Charlotte Dial, is trying to coach a first-grade girl through a math problem. But the girl isn't getting it — and Dial gets angry. With the whole class watching, she rips the girl's paper in half and sends her to the "calm down" chair.

"There's nothing that infuriates me more than when you don't do what's on your paper," Dial says loudly. "Somebody come up and show me how she should have got her answer." Then, to the girl: "Do not go back to your seat and show me one thing and then don't do it here. You're confusing everybody."

The video is undeniably upsetting. But the bigger question it raises is whether it happened to capture a teacher's worst moment, or whether it's indicative of a larger pattern.

It's the latest exhibit in a long-running debate about Success Academy and similar "no excuses" charter schools — schools that have gained fame simultaneously for stellar test results and for a culture of strict discipline that supporters say is necessary and critics say is too harsh.

Success Academy is very strict, and it has very high test scores

The New York Times notes that Success Academy's teacher handbook forbids behavior like Dial's, telling teachers not to yell at children, get frustrated, or shame their students. Many teachers at Success Academy are young and inexperienced, in a competitive environment with high expectations, and they work 10- to 12-hour days, which can contribute to burnout and frustration.

Still, Dial was held up by the charter chain as a model teacher, and the Times quotes several other former Success Academy teachers who said ripping up work was a technique used to get students' attention.

No one disputes that Success Academy's rules are strict, down to instructions on how students are supposed to sit (eyes tracking the speaker, hands folded, which you can see in the video above) and zero-tolerance discipline for breaking the rules.

Supporters say this is necessary to help students learn. And it's true that 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."

Eva Moskowitz, the founder of Success Academy, argues those results are a direct consequence of strict discipline policies and high expectations.

Success Academy is a Rorschach test on education reform

The schools receive far more applications from interested families in the charter school lottery than they have seats available. Some parents and teachers defend strict discipline practices at "no excuses" chains as necessary and helpful. (One of the best explorations of this dynamic is in a This American Life episode, where a student who suffered under "no excuses" discipline himself grew up to be a teacher who enforces it.)

But Success Academy has also created a vocal group of former parents and teachers who argue that its classrooms are punitive and that its techniques, even when they succeed, drive out students' love of learning.

Reading accounts of visits to Success Academy schools makes it clear that even if critics and supporters are observing the same classrooms, they're filtering what they see through their own biases.

The New York Times, which has published a critical series of articles on Success Academy, described the schools as exacting, with students marching silently in straight lines in the hallway and teachers who did not hesitate to shame students publicly for low grades or test scores — even if they also praised them lavishly for improving. The article barely mentioned the curriculum.

Education Next, a journal generally friendly to the education reform movement, published an article from the education policy director at the conservative Manhattan Institute, who observed classrooms and praised the rich, challenging curriculum students were asked to master. The article barely mentioned discipline.

Both are probably true: that Success Academy students receive high test scores because much is expected of them and their teachers, and that those expectations, combined with strict discipline codes that would seem out of place at a wealthy public school in the suburbs, can be extremely stressful.

Success Academy matters because it often stands in for the larger charter movement

Success Academy is 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.

This 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.

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.

The criticisms of Success Academy raise issues that apply to the broader charter school movement, or at least to the "no excuses" schools that are celebrated for both their strict discipline and their test scores.

So the video of one teacher behaving very badly in the classroom, if that classroom is at a Success Academy school, can never be about one teacher or one school. It always ends up as an indictment of the charter school movement as a whole.