She teaches English and history at Coliseum College Prep Academy in East Oakland, but Becca Rozo-Marsh knows how to do the math.

She could earn more money by leaving Oakland Unified School District and getting a job in another school district. Even so, Rozo-Marsh wants to continue working in the community where she’s gotten to know the families of her high school students over seven years.

“I know there are a lot of teachers that are being forced to leave,” said Rozo-Marsh, who was raised in El Cerrito and graduated from Berkeley High School. “They want to make the choice to stay, and they can’t afford to live here.” But leaving “destabilizes our schools.”

Oakland pays teachers a starting salary of roughly $46,000, while nearby San Leandro Unified pays $60,000, Hayward Unified pays $61,000 and Fremont Unified pays $65,000, according to the California Department of Education. Differences in the way benefits are offered may mean the amounts can’t be directly compared.

Even so, it’s barely enough to get by in Oakland, where the average rent is $2,527, according to RentCafe.com, a real estate tracking website. Rozo-Marsh and a friend own a home in Oakland’s Laurel district, but they have roommates.

“To afford our mortgage in Oakland on the salaries we have, we have six people living there,” she said.

Oakland public school teachers have been working without a contract since July 2017. Negotiations on a new contract have gone on so long that teachers have threatened a citywide strike.

Teachers I’ve spoken with, including Rozo-Marsh, argue that the school district is underfunding classroom education and that teachers are paying the price. The next negotiation session is scheduled for Wednesday. A strike is likely if demands aren’t met, according to the Oakland Education Association, the teachers union.

Oakland teachers are demanding smaller class sizes. Rozo-Marsh has two classes with more than 30 students in each. Teachers have requested a 12 percent raise over three years. The school district countered with about a 2 percent increase over three years.

That’s not enough to make the district attractive for teaching talent. Even some district representatives agree that the teachers are justified in asking for more money. But Board of Education member James Harris told me the district can’t afford to do right by its teachers.

“Our problem, as a district, is that we are too large. We operate too many schools,” Harris said. “What we won’t do is put ourselves and our city on the hook for money we don’t have, so we have to be thoughtful and smart about how we’re doing this.”

So far, the district hasn’t been thoughtful or smart. Oakland Unified has been hemorrhaging money for years. It faces a $30 million budget shortfall next year and a $60 million deficit the year after that.

The district is not alone in poor money management. In June, Gov. Jerry Brown signed the Education Trailer Bill, which will provide financial relief to districts across the state. Funding from the bill will cover up to 75 percent of the Oakland’s shortfall next year, up to 50 percent the next year, and up to 25 percent in the third year.

But that won’t necessarily help the teachers.

“Teachers are just sick and tired of being pushed around, and the quality of education is eroding because people aren’t coming into this profession anymore,” said Ismael Armendariz, vice president of the Oakland Education Association.

Teachers are leaving Oakland at an alarming rate. The district reported a teacher attrition rate of 22 percent last year — higher than the 11-year average of 18.5 percent.

According to Armendariz, the district had 571 teacher vacancies last year, and 40 positions remain vacant. Teacher vacancies mean more crowded classrooms, and less time for teachers to spend with individual students.

That’s something Oakland can’t afford. According to the Scholastic Reading Inventory, an assessment of reading performance, only 36 percent of students in the Oakland district were reading at or above grade level in spring 2017. A total of a 41 percent of students lagged more than one year below grade level.

“The district has to do something fundamentally different in order to improve education,” Armendariz said. “We believe that starts with keeping quality teachers in Oakland.”

Teachers want more than a raise, according to Armendariz. They want more control of their classrooms and how money is allocated to schools.

“It’s about fundamentally changing the way the district does business,” he said. “We’ve allowed them for too long to invest in things that haven’t improved student outcomes, and now we’re saying that’s enough.

“This contract is going to be settled this year. We are not going another year without a contract. That is not going to happen.”

I asked Harris, the school board member, what the district will do to avoid a work stoppage, which will hurt the students.

“I hope we can find a place where we understand the reality that we sit in right now,” he said.

San Francisco Chronicle columnist Otis R. Taylor Jr. appears Mondays and Thursdays. Email: otaylor@sfchronicle.com Twitter: @otisrtaylorjr