Nearly 60 percent of schools in Mayor Bill de Blasio’s signature school-improvement program have undergone leadership changes since the program started, according to city data, significantly higher than the 35 percent citywide turnover rate over the same period.

Some of that turnover is intentional: Because de Blasio has opted to revive struggling schools rather than replace them with new ones, a key improvement strategy is to change their leadership. It’s also crucial to have strong leaders running schools in the $383 million “Renewal” program since the job requires coordinating the longer school days, new classroom materials and partnerships with social-service providers that come with it.

But leadership churn can also cause problems. Research suggests it can be especially harmful to low-performing schools, contributing to higher rates of teacher turnover and lower student achievement.

At the same time, the pressure of turning around a low-achieving school on a tight timeline has prompted some principals to leave the system on their own accord, leaving vacancies that can be hard to fill.

“If you think that the leader of a school is not effective then you have to replace them,” said Jason Grissom, a researcher at Vanderbilt University who has studied principal turnover in multiple states. “But then you’ve created a turnover event which can have downsides in the short term. It’s tough for a district.”

Of the 78 current Renewal schools, 45 have seen at least one leadership change — including ten with new principals this fall.

Aimee Horowitz, the superintendent in charge of the Renewal program, said she is not concerned about the rate of leadership turnover, adding that local superintendents weigh their options carefully when replacing principals.

“That’s always a balancing test,” Horowitz said. “We have to think about whether the new principal is more likely to impact change than the principal who is leaving.”

City officials would not say how many Renewal principals were replaced because their superintendents determined they were ineffective compared with the number who retired or quit for other reasons. But regardless of why principals ultimately leave, the education department must convince new leaders to take their place, running schools that are under intense pressure to improve.

At times, the city has resorted to unorthodox staffing arrangements to fill principal vacancies in Renewal schools with leaders they believe will be successful. In one unusual example, the education department coaxed a principal to run Boys and Girls High School, a Renewal school, without giving up his post running a separate higher-performing school — an arrangement that later fell apart.

But as the Renewal program has become more established, Horowitz said, it has been easier to find principals to take on the demanding role partly because word has spread that those schools get extra funding, social services, and support staff.

Several new Renewal principals previously were Renewal program staffers, though Horowitz declined to offer a number.

“We’re past the point of having to convince people to take the position at Renewal schools,” she said. “They’re aware that they’ll be supported.”

Principal Geralda Valcin said she was excited to begin leading a Renewal school, despite the tough task of steering the school back on track. About a year and a half ago, she took over the Coalition School for Social Change in Harlem — which had one of the highest dropout rates in the city — after completing the city’s now-shuttered Leadership Academy training program.

One of the biggest challenges, she said, was raising expectations of teachers and convincing veteran educators who had “been doing the same thing the same way” to adopt new teaching methods.

“I felt like I was stepping into a situation where my predecessor and I had different views,” she said. “You have to take what’s working and figure out the rest.”

Finding effective principals to run the city’s lowest-performing schools has been a persistent challenge.

Under former Mayor Michael Bloomberg, the education department closed many lower-performing schools, and tried to entice talented leaders — sometimes with offers of salary bumps — to open new small schools where they could start from scratch and hire new teachers.

To create a pipeline of principals, that administration also launched the Leadership Academy, a fast-track training program to funnel leaders from various fields into high-need schools with the promise that they would have lots of freedom in choosing how to run their schools.

Still, the Leadership Academy only ever met a fraction of demand, and officials later stepped back from the practice of offering bonuses, finding that it did not seem to draw more effective leaders.

Under Mayor Bill de Blasio, the city has ratcheted up the amount of experience required to become a principal, and has eschewed the school closures and new school openings that gave principals a chance to start fresh. Instead, the city has bet on giving existing schools more resources and principals more specific instructions on how to revamp floundering schools.

Marc Sternberg, a former deputy chancellor in the Bloomberg administration who previously ran a struggling school in the Bronx, said it is hard to improve troubled schools if their leaders leave quickly or have limited autonomy.

“We are asking some very courageous people to do an impossible job,” said Sternberg, the director of K-12 education for the Walton Family Foundation. (Walton is one of Chalkbeat’s funders.)

“Throw in principal turnover — where the vision-keeper is rotating,” he added, “and you’ve got the inevitable confusion and slippage that that generates.”

Still, some teachers in Renewal schools said principal transitions have brought positive changes.

At J.H.S. 8 in Queens, also called New Preparatory Middle School, one veteran educator said the school’s former principal was disorganized, sometimes sprang new programs on teachers at the last minute, and at one point used a rotating cast of long-term substitutes instead of hiring new teachers. (The former principal did not immediately respond to a request for comment.)

But after assistant principal Katiana Louissaint took the helm this fall, morale started improving, said the teacher, who asked to remain anonymous. After a recent round of parent-teacher conferences, teachers stuck around to chat with each other, a rarity under the former principal.

“At the end of the night,” the educator said, “the teachers weren’t running for the door.”