Roosevelt High student Demetrice Lester, 18, transferred to the neighborhood school after leaving KIPP DC College Prep in the winter. (Matt McClain/The Washington Post)

More than 10,000 students transferred into or out of the District’s public schools during the 2013-2014 school year, a massive ebb and flow that experts say is linked to lower achievement and faltering graduation rates.

The churn was particularly acute in the city’s comprehensive high schools, where rosters grew by as much as 30 percent, according to individual school data on student mobility released by the Office of the State Superintendent of Education (OSSE). Students came and went from other countries, from other schools, from neighboring districts, from jail. They stayed for a day or a few weeks, or for the rest of the year. Many who left disappeared from the city’s records completely.

Experts say that such high levels of movement create disruptions and distractions at a time when students are at the greatest risk of dropping out of school. They make schooling more difficult for children and teens, interrupting routines, learning, and formative relationships with friends and teachers. The flux is also hard on schools, as teachers and counselors must constantly adjust to changing classrooms.

“We’re used to it,” said Amber Oliver, a 10th-grade English teacher at Roosevelt High, a neighborhood school in Petworth that started the 2014-2015 school year with 487 students, enrolled 73 more by May and had 47 students withdraw. “We are an open-door school. Students that nobody else will take, we will take them.”

Among those who enrolled in the spring — some just weeks before the school year ended — were a 17-year-old from Guatemala returning to classes for the first time since he was in sixth grade, a ninth-grader who left a nearby charter school after she was caught with marijuana, and an 18-year-old who dropped out of Southeast Washington’s Ballou High earlier in the year after moving into a group foster home in Northwest Washington.

Often, transient students bring complex challenges that can take schools time to identify and begin to address. They present additional challenges in a city such as Washington, which already struggles to educate its most at-risk students and where thousands of children are homeless or have family instability.

According to a 2010 Government Accountability Office report, about 13 percent of students nationally changed schools four or more times by the eighth grade. The most mobile students were disproportionately poor, black and came from families that did not own a home. The report found that about 12 percent of the nation’s schools had high rates of mobility, with more than 10 percent of students leaving their school during a single year.

Dozens of schools in the District gained or lost the equivalent of 10 percent of their enrollment, according to the OSSE data.

The District also is a national leader in school choice, with 44 percent of students enrolled in public charter schools and a lottery system that allows students to enroll in traditional schools throughout the city. Policies that allow for expansive school choice — which communities across the country are beginning to embrace — are intended to improve educational opportunities. But some say they have an unintended consequence.

“They promote the idea that you can change schools at will,” said Russell Rumberger, a professor of education at the University of California at Santa Barbara who studies mobility.

Jennifer Niles, the District’s deputy mayor for education, said that the District needs to do far more work to understand why students weave in and out of the city’s schools and across state lines into Maryland and Virginia. She wants to identify schools that are successful at holding on to potentially transient students to better understand how they do it.

Routine school changes­ typically happen during the summer, when transitions are easier to manage ahead of a new school year. Midyear transitions are far more disruptive.

A Roosevelt High student walks through a hallway in the school’s temporary quarters in the former MacFarland Middle School building.The 1930s-era school is undergoing a $130 million renovation. (Matt McClain/The Washington Post)

In the District, traditional schools bear the brunt of mid­year turnover. Many charter schools do not admit students after the beginning of the school year, while neighborhood schools are required to enroll students at any point.

During the 2013-2014 school year, the school system’s enrollment grew by 2 percent — with 3,175 students entering midyear and 2,226 leaving — while charter schools’ enrollment declined by 5 percent — with 1,306 entering and 3,164 leaving, OSSE data shows. Among high schools, nearly every traditional high school gained students, while every charter school lost students.

Cardozo Education Campus, a public school that serves sixth- through 12th-graders, had the highest influx, with a 30 percent enrollment increase due in large part to a growing number of immigrant students; the Northwest Washington school’s net gain was about 18 percent, as scores of students withdrew during the same year. National Collegiate Preparatory, a charter school in Southeast Washington, lost the equivalent of 14 percent of its students, partly due to a policy that automatically withdraws students who have been absent for 25 days, said Jennifer Ross, the school’s founder and executive director.

Demetrice Lester, 18, said that coming from a charter school, the churn at Roosevelt was striking. He left KIPP DC College Prep in the winter after his grades fell and he thought he couldn’t catch up, he said.

“At KIPP, you saw the same people every day. The same kids. It’s kind of like a prep school. Everybody’s parents are on them,” he said. “Here, a lot of kids don’t really come to school.”

Brian Wiltshire, an Advanced Placement English teacher at Roosevelt, said he starts the school year teaching Plato’s “Allegory of the Cave,” discussing rhetorical devices, what’s real and what’s not, and how education shapes your perspective. It’s a lesson he likes to refer to throughout the year. But he often looks out at his class and sees several students who don’t know what he’s talking about.

“Everything we do in class is inter­connected,” he said. “If you can’t make those connections, they are only seeing a piece.”

Teachers at Roosevelt said they help new students get up to speed by customizing lesson plans and offering time for makeups. Wiltshire said he stays at school until 8 p.m. four nights a week to assist students.

The students who transfer in late are often less likely to come to class, he said.

All the coming and going has a cumulative effect. Of the 123 ­seniors who graduated from Roosevelt on June 12 or are scheduled to graduate in August, just 27 started at the Northwest Washington school at some point during their freshman year; 78 percent of the graduates spent three or fewer years in the school.

After many years of viewing student mobility as a family problem that schools could do little to control, more school districts are focusing on the issue, Rumberger said.

Along with the District, a handful of states, including Colorado and Rhode Island, have begun reporting data on mobility. California is developing a system for holding schools accountable for students’ academic progress even after they change schools.

Niles hopes to reduce mobility by changing the way schools are funded, devising a system that pays schools according to actual enrollments.

A charter school’s funding is based on October enrollment, no matter how many students the school loses or gains throughout the year. Traditional schools receive funding based on projected enrollments from the previous spring. Critics say the system encourages traditional schools to inflate projections and charter schools to let go of students after their October audits.

Cathy Reilly, a longtime advocate for District high schools, said possible solutions are more complex: “We have to change the culture at schools, so we really make it more attractive to stay, and get rid of this whole mentality that the answer is to just go find something better.”

Students enrolling at Roosevelt during the past two years entered a school that already has a makeshift feel. The school has been operating in temporary quarters in the former MacFarland Middle School building while the 1930s-era high school undergoes a $130 million renovation next door.

The reopening of Roosevelt was recently pushed back until the fall of 2016. The new school will feature a dual-language track and a global studies program, as well as a proud new facade.

For now, students make do in the aging building next door with bars on the windows and storage boxes in the hallway, while bulldozers and cranes outside promise something better.

Antony Santay, 17, said he was looking for a fresh start when he transferred in February from DuVal High School in Prince George’s County, where he had been suspended multiple times and was going to school “about once a month.” He moved in with his mother in the District and enrolled at Roosevelt.

“I didn’t want to be a nobody in life,” he said. It was strange to walk into a place where he did not have any friends, but he said he started going to school every day and by spring he had A’s and B’s on his report card, something he hadn’t seen in years.

In the fall, he said, he’ll come back to Roosevelt.

“I’m doing better,” he said. “I think it’s better if I stay.”