A Fairfax County elementary school principal will resign her post on Jan. 1 after mounting concerns from parents and staff this fall involving teacher morale and turnover.

Barbara Leibbrandt will retire after 29 years with the school system, including the last four at Fort Hunt in Alexandria, assistant superintendent Deborah L. Tyler announced Monday.

In a letter to Fort Hunt families and teachers, Tyler wrote that beginning Jan. 6 Leibbrandt will be replaced in the interim by Janet LaBel, a retired Fairfax principal who served at Cub Run elementary.

“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 permanent successor will begin in the meantime.

Earlier this year, parents and staff members at Fort Hunt began questioning Leibbrandt’s leadership. When the school year began in September, about 40 percent of the staff were new to Fort Hunt. Many of the departed teachers cited morale issues at Fort Hunt, which some described as a toxic work environment. Many families and teachers called for Leibbrandt’s ouster.

A working conditions survey by Fairfax school employees ranked Fort Hunt 138th out of 139 elementary schools in the county. JoAnn Karsh, executive director of the Fairfax Education Association, the largest teacher organization in the county, wrote a letter in July to new superintendent Karen Garza about concerns at the school.

Fort Hunt parents and teachers described the school as a “joyless place that has become a bad place for learning,” Karsh told The Post in September.

In response to a Post article published in September, Tyler wrote to parents that she remained committed to the school.

“Each child at Fort Hunt Elementary School deserves our unwavering collective effort,” Tyler wrote.

Announcing Leibbrandt’s retirement Monday, Tyler wrote: “We certainly wish her the very best in all of her future endeavors.”