The Denver school district isn’t soliciting any new schools this year. Once the country’s fastest-growing urban district, Denver’s enrollment has plateaued.

What’s more, the district isn’t looking to replace any struggling schools next year. Instead, it is asking schools with chronically low test scores to follow improvement plans.

The strategy departs from the “portfolio model” of managing schools, which calls for giving schools autonomy, allowing families to choose among them, and then closing or replacing schools if they don’t make the grade academically.

Denver is known nationwide for its adherence to the model. But when district officials declined to order the replacement of any low-performing schools last year, either, some portfolio proponents began to question whether Denver was setting itself up to undo the academic gains it had made.

Denver’s shift away from school closure comes after backlash against a district process that relied heavily on student test scores to determine whether to shutter struggling schools. The process was inflexible: If schools failed to perform, they would be closed or replaced.

Teachers and parents complained the process didn’t consider other important factors, such as a school’s culture, what it did well, or the type of students it served. School board members felt the rigid criteria didn’t allow them to exercise their judgment.

A new process rolled out this school year will change that. In late December, the school board approved improvement plans for three schools with persistently low student test scores: Stedman Elementary School in northeast Denver, Lake Middle School in northwest Denver, and Compass Academy, a charter middle school in southwest Denver.

Stedman and Lake will have two years to bring up student test scores. Compass, which has the poorest academic track record of the three, will have one year. The school board will consider improvement plans for seven other low-performing schools this month.

Opinions on this type of approach are mixed. Some charter school advocates don’t like it. They’d prefer the district close struggling schools where few students are reading or doing math on grade level. That would make room for new schools that advocates believe could do a better job — oftentimes, schools run by independent charter networks with a track record of high test scores.

But other powerful forces, including the Denver teachers union and the hundreds of parents whose children have been affected by school closures, vehemently favor an approach that helps low-performing schools instead of punishing them.

That sentiment was on display at the Denver school board meeting in late December. Parents from Stedman, Lake, and Compass spoke glowingly about their schools and asked the board to give them more resources and time to show academic growth.

“We have an amazing plan in place and we need your support,” said parent Janeel Williams, who has a fifth-grader at Stedman. “Please support our journey.”

Williams quoted a song she said happened to come on the radio every time she and her son were driving to school: “I don’t know the entire song but the hook is, ‘Nothing can stop me, I’m all the way up.’ Stedman, hello! Nothing can stop us, we’re all the way up!”

While the lack of school closures this year contributed to the district’s decision not to solicit any new schools, officials gave most credit to another factor: slowing enrollment growth.

Denver’s student population has swelled by more than 14,000 students since 2010. But growth has been flat in recent years, and demographers are predicting it will soon plunge.

The main reasons for the predicted drop are decreasing birth rates and increasing housing costs, which are pushing families out of the city. The district has 93,356 students this year in preschool through 12th grade, according to recently released district data. In five years, third-party demographers say Denver’s enrollment will shrink to 88,785 students.

In an open letter to school developers, Jennifer Holladay, who oversees the district’s annual “call for new quality schools,” wrote that the enrollment landscape makes it difficult for new schools.

“Several approved new schools have not opened on their original timelines, or not opened at all,” she wrote.

The reason is often financial. Denver schools are funded per student, and if new schools can’t attract enough of them, the schools won’t have the money to hire teachers and buy supplies. (The district allows families to request to attend any school in the city.)

Denver currently has approved 31 new schools that are not yet open. The majority — 22 of the 31 — are charter schools.

Three of the 31 schools are scheduled to open this fall, including a new district-run middle school in the family-friendly Stapleton neighborhood, which is one of the only places in the city with open land for developers to build more single-family houses.

But the other 28 schools “on the shelf” don’t have projected opening dates.

In her letter, Holladay noted the district’s enrollment landscape is tough on existing schools, too.

Two charter schools, Venture Prep High School and the middle school at Wyatt Academy, which had been a K-8 school, closed at the end of last school year. (Wyatt Academy’s elementary school, which had more robust enrollment, remained open.)

Another charter school, Roots Elementary, recently announced that it will close this spring. Declining enrollment was a factor in all three cases.

The district is still obligated by state law to accept applications for new charter schools. That deadline is April 1. If new charters are approved, they are free to open in private buildings.

But school real estate in Denver is both rare and expensive. When the district solicits new schools, as it did with the middle school in Stapleton, it allows those schools to open in district buildings. At this point, that offer isn’t on the table for the fall of 2020.

Clarification: A previous version of this story said this is the second year Denver is not soliciting new schools. District officials initially said they did not need any new schools last year, but changed course when new data showed a need for a new middle school in Stapleton, as is mentioned in the story.