More than a third of the staff members at a Harlem charter school run by the Success Charter Network have left the school within the last several months, challenging an organization that prides itself on the training and support it offers its teachers.

The unusually high turnover at Harlem Success Academy 3 and the network-wide issue of teachers quitting mid-year led the founder and chief executive of the Success Charter Network, Eva S. Moskowitz, to express concern in an October newsletter.

“This is not a ‘gig’ ” she wrote, informing staff members that by breaking their commitment to the schools and families midyear, they were acting unethically.

At Harlem Success Academy 3, 22 of the school’s 59 administrators, teachers and classroom aides left between the end of the last school year and the beginning of this one, according to the school’s records. Some took jobs at other schools, some moved to new cities and some said they quit out of frustration with the school’s tightly regulated environment.

The loss of more than 30 percent of its teachers distinguishes the school within its network of six other schools, where turnover is less common. At Harlem Success Academy 1 and Harlem Success Academy 2, the attrition rates were about 19 percent between June and this month. And at the network’s two Bronx schools, few faculty members left.

Charter schools have generally experienced relatively high teacher turnover. From 2008 to 2010, charter schools’ average attrition rate was 25 percent and district schools’ was 14 percent, according to state data.

Among those who left Harlem Success Academy 3 was the school’s principal, Emily Rodriguez, and its assistant principal. Ms. Rodriguez is now the director of literacy for Explore Schools, a growing network that now has three charter schools in Brooklyn. Seven Harlem Success Academy 3 teachers have also departed for jobs at Explore Schools between June and this school year.

Ms. Moskowitz said the teachers left in part because Ms. Rodriguez was a popular principal, and in interviews, several teachers supported the explanation. The teachers said Ms. Rodriguez’s departure, which followed a maternity leave, had prompted some teachers to look for work elsewhere.

Ms. Moskowitz said some staff had also quit to pursue graduate school or move outside the city.

“It’s hard for kids and families when you have an exodus,” she said. “My focus when this happened was really to make sure that it’s a great school and the kids had teachers when they started.”

She said that the school is doing well under its new principal, Richard Seigler, a former dean of students and teacher at Harlem Success Academy 4. At 25, Mr. Seigler is one of the city’s youngest principals.

Few of the teachers who left Harlem Success Academy 3 would speak about why they quit, and those who did refused to be named, citing fear of retribution or concern that they could lose their new teaching positions.

Morty Ballen, the founder and chief executive of Explore Schools, said he had not intentionally poached Success Academy’s teachers.

One former Harlem Success Academy 3 teacher who quit at the end of last school year said she had left because she felt “micromanaged.”

“You couldn’t teach in the way you wanted to teach,” she said. “If your kids weren’t sitting perfectly, looking straight at the teacher, not saying a single word, then you weren’t doing your job.”

Monica DeFabio, a third-grade teacher who is in her second year at Harlem Success Academy 3, said she did not know why many of her former colleagues left. “I really can’t say anything has suffered,” she said. “Richard’s come in, and he’s hit the ground running.”

Ms. Moskowitz said she was aware that some teachers had left because they wanted to work in a different type of school, yet she stressed that with 57,000 applications for 256 jobs this year, her schools were in demand.

“We believe in teacher choice just like we believe in parent choice,” she said. “Some teachers want a single-sex school, or a progressive model, or a traditional model of education.”

In her October newsletter, Ms. Moskowitz said that the network was working hard to retain its teachers, but had struggled this year with the issue of teachers quitting after school was already in session.

“We have had a number of teachers quit the night before schools starts — after midnight!” she wrote. “We have had teachers quit two weeks into school. A quick e-mail reads ‘sorry for the inconvenience. …’ ”

It is not merely a logistical predicament, the message continued. “Breaking your commitment in the middle of the year is a big deal and frankly, unethical,” Ms. Moskowitz wrote.

Available data does not indicate how many of the network’s teachers left in the middle of this or last school year. In an interview, a former Harlem Success Academy 1 teacher who quit several months into last school year said it was a decision she made only after realizing there was an impassable gulf between how she wanted to run her classroom and the teaching and discipline methods her supervisor insisted on.

By the time Thanksgiving rolled around and she decided to leave, several other Harlem Success Academy 1 teachers had already quit, she said.

“I got the impression very early on that there were a lot of people wanting my job and that if I left, they would find someone else to do it,” she said.

This fall, the Success Academy Network opened two new schools, one in Bedford-Stuyvesant, Brooklyn, and the other on the Upper West Side of Manhattan. Next year, Ms. Moskowitz plans to open three new schools in the Brooklyn neighborhoods of Cobble Hill, Bedford-Stuyvesant and Williamsburg.