Updated Monday at 6:22 p.m.

After two-and-a-half turbulent years as superintendent of Boston Public Schools, Brenda Cassellius will resign in June, city officials announced Monday.

Just last summer, the school committee renewed Cassellius' $311,000-a-year contract through June 2024. She started in the position in July 2019.

Boston Mayor Michelle Wu, who took office in the fall, said she and Cassellius reached a mutual decision on her departure. She'll finish out the school year.

"I am grateful to you — the entire BPS community of families, partners, supporters and loyal critics," Cassellius wrote in an open letter to the BPS community. "Your insight and wisdom, and your willingness to share hard feedback made our decisions better and our work more impactful."

Cassellius is the city's fourth superintendent, including two interims, appointed in the last decade. She had a bumpy ride in the role, juggling the many demands of the state's largest school district. Eight months into her tenure, the pandemic forced the closure of public schools. Since then, she has faced union lawsuits, no-confidence votes and angry parents who thought she did not do enough to encourage remote learning or did too little to bring students back into classrooms quickly enough.

Most recently, she faced criticism from the state and from public school nurses about the coronavirus spreading in the schools, including an outbreak at the Mary Curley School in Jamaica Plain that forced the K-8 school to close temporarily and left her at odds with state officials. More recently, she put three underperforming schools on intervention status as a way to stave off the threat of state receivership.

Tom Scott, executive director of the Massachusetts Association of School Superintendents, said the average tenure of a Massachusetts superintendent is about five years. That's longer than Cassellius' time, which will amount to three years when she vacates to role in June.

"That's really insufficient for them to have sort of long-term effect in terms of sort of creating sort of the vision policy and direction the district needs," Scott said. "So there is a problem with, in general, with the way in which this role of superintendent is being used today. I think it really needs to be looked at if we think we're going to have people served in these communities for any extended period of time."

Wu said she does not plan to hire an interim superintendent, and plans to instead begin a search for Cassellius' successor right away.

Kim Parker, president of the Black Educators Alliance of Massachusetts and a parent of a BPS student, said the conversation about the next superintendent will absorb more time and energy, diverting attention from existing problems, like the children who aren’t reading at grade level or what summer school will look like in 2022.

“I’m so annoyed and frustrated we have to do it again,” Parker said of the superintendent search. “Our kids get older, there’s no one at the top. What all parents want is someone who’s going to do right by our kids.”

The mayor called Cassellius an "incredible champion for our children and for equity," in her own letter to BPS students, staff and families. She cited Cassellius' guarantee to get every school access to a social worker, family liasion, guidance counselor and librarian. She also cited the progress she made toward greater equity, inclusion and justice by reforming school policies.

That includes a historic change in how the city's three elite exam schools admit students. The Boston School Committee voted unanimously last summer to change its admissions policies at the three high schools, overturning a system that had existed for decades, in an effort to make the schools more diverse and more reflective of the city's racial, geographic and economic diversity.

Under the new policy, the exam schools made grades more important than entrance exam scores, while creating socioeconomic and geographic tiers for admission that widened the pool of applicants.

Cassellius called the changes a "huge step forward for our students."

"My personal position, every student should have equal opportunity to access," she said the night of the vote. "It's who I am. It's how I lead. It's what drives me to do this work even on difficult days."

Ruby Reyes, executive director of the Boston Education Justice Alliance, credited Cassellius with setting the stage for the changes in the exam school admissions process.

“I think the exam school decision is a huge, huge thing that we were all really surprised at, but really grateful for,” Reyes said. “It’s not perfect, but it’s like two steps forward.”

Former Mayor Marty Walsh appointed the school committee that named Cassellius as superintendent in 2019. She was a former education commissioner in Minnesota and moved to Boston for the job.

The city’s Build BPS program, launched under the Walsh administration to rebuild and renovate city schools, currently has no new building projects underway, Reyes said. Staff turnover plagued Cassellius’ administration, and principals were relocated without community input.

“It’s no surprise the schools that are struggling have the biggest population of Black and Latino students, English learners and students with disabilities. That’s the inequity of Boston,” she said. “How do you do the work to make sure that’s where you put the most resources? Or do you pretend that the exam schools are your priority?”

The next superintendent, Reyes said, will need to have a “clear, bird’s-eye view” of how to fix a system that leaves Black and Latino children at a disadvantage and parents distrustful.

Paul Reville, a former secretary of education in Massachusetts, called Cassellius' departure a loss. The pandemic loomed large over her tenure, and so did Wu's political ascension when former Walsh departed office last year to become U.S. Labor Secretary in President Joe Biden's administration.

"She tackled tough issues, like the exam schools, which is not a popular topic. It's kind of a no-win topic for leadership in the school system," he said. "She had the courage to come at that."

Reville said Cassellius also fixed a district that had 34 different graduation requirements, streamlining them into a single clear goal aligned with what the state says is essential for success in college. He also noted the most recent crisis: an audit showing that city graduation numbers may have been calculated incorrectly, saying she inherited that situation.

"Y'know, she may not have been the perfect superintendent. But at the same time, who would have been in this moment?" Reville asked. "Superintendents are dropping like flies all across the country, as a result of the pressures brought to bear from COVID."

This article was updated with additional comments.