A few months ago, the leader of the city’s largest charter network apologized for a “Got to Go” list of student names created by one of its principals, calling it an anomaly at an emotional press conference.

On Friday, after the New York Times published a video showing a Success Academy teacher lashing out at a first grader, Success CEO Eva Moskowitz again sought to portray the behavior as an isolated incident. But she also mounted a forceful defense of the network’s teachers and its methods, while criticizing the Times’ reporting as biased.

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“I’m tired of apologizing,” Moskowitz said at a press conference. Calling the video “an unfortunate moment,” she said, “Frustration is a human emotion. When you care about your students so much … and you want them to go to college and graduate, it can be frustrating.”

The video, which is just over a minute long, shows teacher Charlotte Dial yelling at a student who didn’t count correctly. As the student tries to correct her response, Dial rips the student’s paper and tells her to go sit away from the other students. A moment later, she tells the class, “There’s nothing that infuriates me more than when you don’t do what’s on your paper.”

Moskowitz’s less apologetic tone illustrates the recent pressure Success has faced after a wave of negative press, including the coverage of the “Got to Go” list. Critics have long held, and Success has denied, that the high-performing schools have done well because they pressure poor-performing or poorly behaved students to leave — claims that the “Got to Go” list seemed to vindicate.

Success has always maintained that its learning environment is rigorous and its discipline policies are strict.

But the video of Dial spread quickly on Friday, and shocked many viewers, who saw the teacher’s behavior as overzealous and harmful to the young students.

“That’s the kind of moment a kid will remember into old age,” one commenter wrote. “Why would a student take another learning risk again? Or anyone who witnessed that?”

Moskowitz said that Dial had been suspended and received an extra week of training. On Friday, she said she would not “throw Charlotte Dial under the bus.”

“She has helped hundreds of children thrive and be successful,” Moskowitz said, flanked by more than 150 Success teachers, administrators, and parents.

Natasha Shannon, the parent of three students in Success schools who attended, said she believes in Success’ mission, including the disciplinary policies.

“I think [discipline] is necessary,” she said. “People who don’t like it, they don’t have to send their children there.”