Hilary Elfman is the kind of teacher San Francisco Unified School District needs to keep, but the odds of that happening decrease every time the special-education teacher surfs the Internet looking for housing she can afford.

The 29-year-old quit an unsatisfying career in advertising to get her teaching credential, hoping to find a calling that “had more of an impact on people’s lives.” She’s in her first year at San Francisco Public Montessori Elementary in Pacific Heights, working one-on-one with 22 special-needs children. It’s a position that’s hard to fill in any school district, let alone one in a city with insane housing prices.

The school days are rewarding, but the nights are frustrating. She makes $57,000 a year and cannot afford a single apartment that’s available in San Francisco. For now, she stays in her parents’ guest room, but that’s not a viable long-term solution. At least the guest room actually exists, which is more than can be said about the school district’s long-promised teacher housing.

“There was some movement toward teacher housing, but it’s not affecting anyone who’s currently working,” Elfman said. “It’s kind of this future thing, but for those who are working now and serving the students now, there just aren’t very many options.”

Teacher housing in San Francisco has been “this future thing” for at least 13 years, back when a one-bedroom apartment in the city could be had for around $1,600 instead of today’s median asking price of more than twice that.

In 2004, Stuart Stoller, then an architect and father of two kids in the city’s public schools, wrote a master’s thesis detailing how the San Francisco Unified School District could turn its unused real-estate holdings into teacher housing. The school board and teachers union backed the plan, and the district pledged to select the most suitable site.

So much time has passed, Stoller is retired, his kids have grown up, and he has three grandchildren. Teacher housing, on the other hand, is still an embryo.

“Obviously, there’s still clearly a political problem with moving forward with this,” Stoller said. “I didn’t pretend that it wouldn’t be a very difficult and problem-strewn thing to try and do. On the other hand, other districts have done it, so it’s not impossible.”

But San Francisco officials are still looking for a suitable site. Why is it taking so long in a small city with a finite number of district-owned, unused parcels to consider? It’s not like searching for a needle in a haystack — it’s more like searching for a needle among 10 needles.

There are roughly 10 surplus property sites owned by the district, including — who would have thought? — the plot at Seventh Avenue and Lawton Street that houses Clancy’s Christmas tree farm and Halloween pumpkin patch.

For years, district officials blamed laws prohibiting affordable-housing funds from being used for particular occupations, but then-state Sen. Mark Leno solved that problem with legislation allowing teacher housing to go forward five months ago. Still, nothing.

Shamann Walton, president of the school board, did his best to explain. He said building housing is expensive, and the district wants neighborhood buy-in before committing to any particular site. (Note to San Francisco NIMBYs: If you oppose even school teachers living in your neighborhood, you are seriously selfish.)

“I wish it was as simple as, ‘We have district property, let’s just go build on it,’ but the financing piece is important and making sure the surrounding community is on board is important,” Walton said. “I can’t give you a specific timeline, but I will say we’re committed and working very hard to making this a reality for our educators.”

Surely, Mark Sanchez, who was on the school board back in 2004 and who regained his seat in November, can explain why teacher housing has stalled.

“I wish I knew,” said Sanchez, who’s also the principal at Cleveland Elementary.

For all these years, Sanchez has backed an aggressive plan: building up to 1,000 homes for teachers and aides at the current site of the School of the Arts on Portola Drive. This can’t happen until the high school moves to its long-slated new site at 135 Van Ness Ave., which means the teacher housing wouldn’t be ready for at least five years.

“If we don’t start now in making the plans, it’s always going to be five years out,” Sanchez said. “It’s very frustrating.”

Time is most certainly of the essence. Contract negotiations between the district and the teachers union begin Tuesday, and the district already needs to fill 664 certificated positions for next year, including 465 classroom teachers, as well as nurses, counselors, librarians, social workers and others. That doesn’t include an untold number of lower-paid classroom aides who are also expected to leave the district. As of last month, 22 classrooms around the city lacked permanent teachers.

A working group to discuss teacher housing — with members from the school district, teachers union and the Mayor’s Office of Housing — hasn’t met in two months and has no meetings scheduled. The head of the district’s real estate division has announced his intention to leave, and the district is looking for a replacement.

Dennis Kelly, the former president of the teachers union, said the district has talked a good game about teacher housing, but has never made a real commitment to building it.

“More than salary, housing is becoming a factor that really will determine whether or not people will come here to work,” Kelly said. “San Francisco has fairly actively moved away from doing anything about it.”

One example cited by Kelly was the 2013 land swap in which the school district gave the city 1950 Mission St., prime property for affordable housing development, and 1101 Connecticut St. in exchange for the parking lot next to district headquarters at 555 Franklin St. and $4.5 million.

The Mission Street site is being used as a Navigation Center for homeless people and is scheduled for affordable-housing development, but not specifically for teachers. The parking lot remains a parking lot for administrators rather than being looked at for housing.

And Hilary Elfman’s home remains her parents’ guest room. Elfman surveyed all her colleagues at school about their living situations, and every single one is reliant on a spouse or family member for housing.

“There is not one teacher here who’s living independently,” she said. “If I were to sum it up, I would just say, ‘Who’s going to teach the children of San Francisco? Who’s it going to be?’”

Probably not Elfman. If she can’t find housing soon, she said she’ll likely move to a less-expensive school district. And the 22 children she works with now, who are emotionally disturbed or have mental health issues or developmental delays, will be assigned a new teacher who can’t afford housing in San Francisco.

“For all the people who are moving to Austin, (Texas), and Portland, (Ore.), and Seattle, I get it now,” Elfman said. “I know firsthand why.”

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