NEW YORK — Two white girls in blackface grunted and swung their arms like apes. They jumped up and down to music playing in the background, moving in front of a camera, sneering as a third girl recorded them.

The six-second video snippet was recorded about 2 1/2 years ago, but it resurfaced this month, thrusting Poly Prep Country Day School in Brooklyn, one of New York City’s elite private schools, into the national conversation about racism.

On Friday, hundreds of Poly Prep students, dressed in black, walked out of an assembly, filtered into the hallways and staged an hour-and-a-half sit-in, which was first reported by the Polygon, the student newspaper.

That same day, on the eve of the holiday weekend honoring the Rev. Dr. Martin Luther King Jr., the video of the Poly Prep students was lumped into a montage of other imagery that swept across social media: a viral video from the University of Oklahoma of a female student with her face painted black and using what sounded like a racial slur, and video of white male students wearing “Make America Great Again” hats who had encountered a Native American veteran of the Vietnam War outside the Lincoln Memorial last Friday. A longer version of that video posted over the weekend led to divergent views about what had actually taken place.

By Saturday, the Poly Prep video had gone viral with the help of an article from The Daily News. On Sunday, Mayor Bill de Blasio weighed in. “Poly Prep has some real explaining to do. And what’s absolutely clear is that a conversation about racism at the school is long overdue,” de Blasio said on Twitter.

“On the King holiday weekend, we are now dealing with blatant racism of a younger generation,” said the Rev. Al Sharpton, whose two daughters are alumnae of Poly Prep. “They’ve been emboldened.”

He added, “We have a problem.”

Jennifer Slomack, a spokeswoman for Poly Prep, confirmed that one of the students involved in the video is no longer at the school, while the other two are. All three students were in sixth grade when the video was made.

Slomack declined to comment further on the students, citing privacy laws.

“We do not tolerate racism or prejudice in our school or in our communities,” she said in a statement. “We took immediate action as soon as we learned of a highly offensive video, taken years ago, being circulated on our campus. It was an egregious violation of our community values and code of conduct.”

Neither of the two students still at the school had been disciplined.

On social media, many critics said that institutions frequently fail to take appropriate disciplinary action regarding these episodes.

At the University of Oklahoma, school officials suggested that an apology from the young woman in blackface and another student could be the extent of punishment. The gesture will fall significantly short of the school disciplinary action against two students who led a racist chant and were expelled in 2015.

Poly Prep is known for its competitive sports program and sprawling, collegiate campus in Dyker Heights, Brooklyn. The lower school is in Park Slope. Notable alumni include Joakim Noah, an NBA player, and Rep. Max Rose, D-N.Y.

New York City’s private schools are overwhelmingly wealthy and white, and are increasingly becoming part of the public dialogue about segregation as the city moves to integrate public schools.

“We should not view this incident of white girls in blackface gyrating as apes in isolation,” said David E. Kirkland, executive director of the Metropolitan Center for Research on Equity and the Transformation of Schools at New York University. “The video perpetuates the sense that black bodies don’t belong in our schools.”

About 39 percent of the 1,083 students in kindergarten through 12th grade at Poly Prep identify as “people of color,” according to data the school provided to The New York Times.

Current and former black students described a culture of intolerance, even as the school promoted diversity. For some, the video was the latest in a string of slights.

“I would like to say I was disappointed,” said Jeovanna deShong-Connor, a senior who is co-president of the student group Umoja, which organized the demonstration Friday. “But I have been hearing hateful speech since I was a freshman.”

She added, “I felt it was my responsibility, our responsibility as the senior class to really do something.”

The events unfolded over a week. On Jan. 11, a freshman posted the video on a private website for students, according to the male student’s mother, who spoke on the condition of anonymity.

She said he felt that taking it to school authorities would not get the same results as making the video public to students. “I’m proud of him for what he did. When you say, ‘See something, do something about it?’ That’s what he did,” she said.

The mother said her son has not received paperwork for registration for next year as other students have. “He just wanted to speak up. Now, he’s the bad guy,” the mother said, crying. “I’m just worried for his future.”

The school responded to the episode with a letter to parents and students that members of Umoja felt was tone-deaf because it emphasized that the distribution of the video violated the school’s code of conduct. “It came out like the sharing of the video was worse than the content of the video,” said Talisha Ward, also a senior and co-president of the student group.

The Monday after the video was posted, school administrators began taking steps to talk to students and faculty members about the video and racism in general through special assemblies and one-on-one conversations. At one gathering, a dean explicitly called the video “racist,” Ward, 17, said. But some students felt that the overall student body did not understand the gravity of the problem. As a result, students began planning what would become Friday’s demonstration.

Parents of one of the students in the video said they were disappointed in how the school had handled the situation.

They said they did not know the video existed until Jan. 11. Afterward, they said, they met with a dean at the school, and later that night, the student began writing an apology, which her parents shared with The New York Times. They said their daughter wants to address her fellow students to make amends.

“They were playing with makeup. Typical 12-year-olds. They were messing around with the makeup. They mixed it all up and packed it on their faces,” said the teenager’s mother, who spoke on the condition of anonymity.

Her father said he had asked his daughter, “Did you know what blackface was at the time? She truthfully told me, ‘No.'”

The video was first circulated among classmates when the student was in seventh grade, and she then recognized that it was offensive and asked people to delete it, her parents said.

“I myself cannot look at this video without being disgusted with my actions and my ignorance at that time,” the student wrote. “Which is why I understand your anger. This email is not to tell you that you can’t feel that way, I just wanted to help people understand how sorry I am for any offense this has caused.”

The teenager’s parents said she had been keeping a low profile and had been eating lunch in the dean’s office to avoid confrontations.

Ward said she did not know for sure who the students were in the video because they were in blackface and were younger than her. “But I’m going to school with them. These kind of people are in our hallways and in our classrooms,” she said, adding: “I think it’s good that there’s a citywide conversation. It’s good that the video is going viral. We want the girls to know that their actions have consequences. Maybe this is some form of justice.”

This article originally appeared in The New York Times.