Many Memphis students started their school year with something important missing from their classroom: a permanent teacher.

About 100 Shelby County Schools classrooms still lack full-time teachers, Superintendent Dorsey Hopson said Monday, the first day of school, after a tour at Bruce Elementary.

“We’ve had 80 vacancies come up over the last couple of weeks,” Hopson said. “There will be a full press for teachers.”

The number of open teaching jobs hasn’t gone down much since the last week of July, when the district had 123 vacancies to fill. But the district is in better shape than it was at this time last year, Hopson emphasized on Monday.

And it’s not the only district with vacancies left open. Metro Nashville Public Schools, a slightly smaller district, has 24 open teaching jobs. Knox County Schools, the state’s third-largest district, needs more than 40 teachers. Across the board, districts are most hurting for special education teachers, though vacancies exist in nearly every subject.

In cases where a long-term vacancy is expected, such as if a teacher is out on disability, Shelby County Schools has reached out to retired teachers to fill the positions, said spokeswoman Natalia Powers. But in cases where the district is still looking for a permanent hire,  substitute teachers are manning the classrooms.

Briana Johnson, a junior at East High School, said her environmental science class had a substitute teacher Monday.

“There wasn’t a plan or anything. We really just sat around,” she said. “It’s not a class I’m planning on keeping, but still, we didn’t do anything today.”

The first days of class establish the tone for the entire year, making even short-term teacher vacancies a long-term barrier to student learning, said Keith Williams, executive director of the Memphis-Shelby County Education Association.

“I don’t know how the district expects to achieve its goals if they don’t have the staff in place,” Williams said.

In a district of high teacher turnover, with 600-800 new teachers every fall, some vacancies are expected, Powers said. Overall, the district retained 89 percent of its teachers and 93 percent of its highest-performing teachers.

“It’s a revolving door in the sense that you have people that have different circumstances – families, pregnancies — so it’s a changing pool, and that’s what makes it a little bit challenging,” Powers said. “I mean, 108 in a pool of 6,000; it’s very good.”

Reporters Grace Tatter and Katie Kull contributed to this report.

Correction: An earlier version of this story stated the number of open teaching positions listed on Metro Nashville Public Schools’ website, about 80. Some of those positions had in fact been filled. The correct number of vacancies is 34.