Sarah Prensky-Pomeranz is the kind of teacher any city would be lucky to have.

The 28-year-old San Francisco native has a master’s degree in education and a teaching credential from Harvard, a pedigree that would surely earn her her choice of teaching gigs.

She’s devoted to social justice and teaches English at Raoul Wallenberg High in the Western Addition, a school where more than 60 percent of students are from low-income families.

She bikes from her apartment in the Inner Sunset at 6:30 a.m. each morning to have time to prepare for her students, who arrive at 7:55 a.m. She stays until 6 p.m. and puts in another two to three hours at home each night.

She makes about $63,000 a year, including a stipend for chairing the English Department plus another few thousand for coaching girls soccer. It’s enough to get by as a single person in a rent-controlled apartment with two roommates as long as she doesn’t splurge on much of anything.

But stay in the San Francisco Unified School District long-term? Raise a family here? No way.

“I feel like it’s the fall of Rome, and I’m seeing it slip away,” Prensky-Pomeranz said of the city becoming increasingly unaffordable for the middle class, particularly teachers. “I think it’s a massive social justice issue that our teachers are paid the way they are. It affects the students to have new teachers every year.”

On Wednesday, Prensky-Pomeranz will finally hear some relatively good news when it comes to teacher pay in San Francisco. Her union will describe to its members the details of a tentative agreement struck with the school district over the weekend that would give teachers an 11 percent raise over the next three years, plus a one-time 2 percent bonus.

The district will also back a parcel tax for the June ballot that, if passed, would cover another 2 percent raise and an additional 1 percent bonus. The Wednesday meeting was supposed to be a strike vote, but its purpose changed after the negotiations wrapped up.

I have a son in second grade at a San Francisco public elementary school that my family adores. If his fantastic teachers had gone on strike, it would have been inconvenient. But I wouldn’t have blamed them a bit.

Even though the newly agreed-upon compensation package is better than many teachers elsewhere in California are getting, it’s still not nearly enough to make up for the financial hole the district has dug for its teachers.

A Chronicle investigation last year found that San Francisco’s average teacher pay — $65,240 in 2014-15 — ranked it No. 528 among 821 California school districts that provided salary data to the state.

At the time, district officials said the data were outdated and that subsequent raises meant teachers are faring better now. But it turns out they’re still not doing well at all.

We crunched the numbers again with the most recent salary data. In 2015-16, 775 school districts reported salary data to the state. San Francisco’s average teacher pay for that school year — $67,540 — ranked it No. 478, alongside the likes of Chico, Salinas and Vacaville.

Teachers in cities where it is far less expensive to live — Fresno, Benicia, Gilroy, San Bernardino and Stockton among them — earn higher average salaries than teachers in notoriously pricey San Francisco.

Christopher Pepper, a coach for the district’s health teachers who also crafts HIV-prevention programs, called the new contract deal a “great start” but said he hopes next year’s parcel tax pushes salaries into the same realm as those in Palo Alto, San Mateo and Mountain View, other districts where the cost of living is as nutty as it is here.

“I’ve seen a lot of my co-workers leave to take jobs in those districts because the disparity is so stark,” he said.

Sorry, but the disparity won’t be addressed by the parcel tax. Not even close.

The average teacher in Palo Alto in 2015-16 was paid about $33,900 more than the average teacher in San Francisco. The average high school teacher in San Mateo made $30,400 more per year. And the average teacher in the Mountain View-Los Altos Union High School District made an eye-popping $53,274 more per year.

San Francisco has a particularly high proportion of teachers with emergency or intern credentials, according to state data, and the teaching force is relatively inexperienced, which could bring down average salary figures. The district, however, still paid mid-career teachers less than 337 other districts.

Members of the city’s Board of Education say these statistics are “shameful,” but they’re the ones who’ve guided the policies that make them reality.

“I understand why teachers are frustrated and angry,” said Matt Haney, a board member running for San Francisco supervisor in District Six. “Our goal should be to have our teachers be among the top paid in the state.”

Officials have explained that the district has prioritized other financial commitments that benefit students, including small class sizes, subsidizing preschool and healthy foods in school meals, and operating more small schools than other districts, each of which requires its own administrative staff.

“We’re working very hard to increase the pay of our educators,” said Board of Education President Shamann Walton, who is running for supervisor in District 10. He added that he was “excited” about the new deal.

Walton said he’s been meeting with philanthropists to encourage them to give more private money to the public schools. Haney wants to see a bigger push for teacher housing and is backing a plan to build apartments on top of a planned new school in Mission Bay.

The district should also conduct an independent audit called for by school board member Mark Sanchez to determine whether money could come from other pots to spend on teacher salaries. This seems particularly prudent, since it will attempt next year to persuade property owners to give the district more money.

All of this and more needs to be done if our super-expensive city wants to keep good teachers, many of whom are now commuting hours each day, renting in-law units without kitchens, renting living rooms in other people’s apartments, and working two or three side jobs after long days in the classroom.

A new report from the National Council on Teacher Quality, a Washington, D.C., think tank that works for tougher evaluations of teachers, analyzed teacher salaries versus the rental and home purchase prices in the 124 largest school districts in the country.

“No big surprise for San Francisco — it’s the least affordable district in the United States in terms of teachers being able to buy a house,” said Kate Walsh, president of the council. “I would have bet $100 on that, but nobody would have bet against me.”

The report found that a new teacher in San Francisco would have to save 10 percent of his or her salary for 30 years to have enough to put a 20 percent down payment on a median-priced home in the city. (And God only knows what houses here will cost in 30 years!)

“The city has made itself unaffordable for anyone on a normal, middle-class income,” Walsh said. “You can always find 22-year-olds who are willing to live in any condition to live in San Francisco, but give them a couple of years and they’re gone.”

That’s exactly the situation Sarah Prensky-Pomeranz finds herself in, saying she can’t envision teaching in San Francisco for more than a few more years. And so the district will see another young, highly educated teacher leave for better pay and cheaper housing.

Over the weekend, she drove three undocumented students to UC Davis to show them the campus and try to convince them they could attend college. She did it for free, because it was the right thing to do.

She was hoping the union would go on strike to make a dramatic statement and was disappointed that it settled for an 11 percent raise, not much different than the deal the district had been offering for months.

“It’s just not enough money,” she said. “We already make so many sacrifices for our job, and it feels like I’m at a point personally where I have to decide between my job and my personal health, well-being and happiness.”

Asked whether she’ll be teaching in San Francisco in five years, she said, “It’s very unlikely.”

Chronicle staff writer Joaquin Palomino contributed to this report.

San Francisco Chronicle columnist Heather Knight appears Sundays and Tuesdays. Email: hknight@sfchronicle.com Twitter: @hknightsf