A Fairfax elementary school principal who served for nearly three decades in the county’s school system plans to resign her post at the end of December amid mounting concerns from parents and staff about morale and turnover at the Alexandria area school.

Barbara Leibbrandt will retire as principal of Fort Hunt Elementary effective Jan. 1, where she had served for the past four years, Assistant Superintendent Deborah L. Tyler announced Monday. Tyler declined to discuss the move.

School officials said Leibbrandt will not return to work before the school’s winter break begins at the end of the week. Leibbrandt was not at Fort Hunt on Tuesday. Reached at her home, she declined to comment.

Many Fort Hunt families expressed surprise at the announcement, but it came just months after parents and teachers publicly described a toxic work environment at the 600-student school, including a lack of communication, fears from teachers about bringing concerns to their superiors and a significant amount of teacher turnover.

This year, about 40 percent of the staff members were new to Fort Hunt, and a survey about working conditions among Fairfax school employees ranked the school 138 out of 139 elementary schools in the county.

But not everyone is unhappy with the school. Parents said the faculty at Fort Hunt is well-regarded and the school has an enviable Spanish language immersion program. PTA President Carrie Sessine said that Leibbrandt’s retirement was met “with a good amount of surprise and disappointment, and a little bit of frustration.”

Sessine said parent concerns about the school didn’t “represent the majority of the opinion.”

School board member Dan Storck, whose Mount Vernon district includes Fort Hunt, said Leibbrandt had done “a wonderful job” and performed “a great service to the school system.” He described her as a principal “deeply committed to children’s education.”

Fort Hunt, in the Alexandria area of Fairfax County along Route 1, serves a mix of middle-class and low-income children. Standardized test scores at the school have been slipping for years, and it was designated as one of 29 “priority schools” in Fairfax, which offers the school more resources but is often a public signal that the school is struggling. Teachers also have reported discipline problems.

Storck said that Fort Hunt “clearly has some continuing challenges” and that the school system’s top leaders had been seeking improvements for more than a year. “Sometimes the best thing to do is move on,” Storck said. “She recognized that it was time to give someone else a chance.”

John Wells, the father of a first-grader at Fort Hunt, said he was aware of some negative views of the school but that he has no concerns. Wells said Leibbrandt “seemed very laid-back, not extremely vocal or in your face.”

Susannah Monteith, the mother of a first-grader, said she initially supported Leibbrandt. She changed her opinion early this school year after a meeting between the principal and first-grade parents about discipline policies and disruptions in class.

Monteith had written a letter about her concerns to Del. Scott A. Surovell (D-Mount Vernon), whose district includes Fort Hunt. During the meeting, Monteith said, Leibbrandt referred to the letter and was “unprofessional” in an exchange with her.

“She just lost her cool,” Monteith said. “She had a bone to pick and did it in public. It was very uncomfortable.”

In a letter to parents and staff members announcing Leibbrandt’s retirement Monday, Tyler said that an interim principal had already been selected. Janet LaBel, a retired Fairfax principal who served previously at Centreville’s Cub Run Elementary School, is slated to take over Jan. 6.

“I am confident she will do an outstanding job in guiding the school in the near term,” Tyler wrote, noting that a search for a successor is underway.