The District’s Anacostia High School saw an enormous fluctuation in its student population in the 2012-13 school year, losing more than one in five students after the first month of school while gaining nearly twice as many during the school year. The enrollment swings left the school with a net student increase of 16 percent.

The numbers offer an indication of the outsize challenge facing neighborhood high schools in the city’s poorest areas, where principals and teachers are tasked with lifting the achievement of a student population that is always shifting.

“We have to constantly get those students reacclimated to our school culture and our instructional and academic expectations,” Anacostia Principal Ian Roberts said. “And that’s one of the biggest challenges.”

The figures were released Wednesday as part of an effort that aims to give parents and policymakers a new way to make side-by-side comparisons of every city school, including charters and traditional schools.

The “equity reports” — a joint effort among the traditional school system, the charter sector and other D.C. education officials — compile reams of data about individual schools that have previously been available only in scattered form, including information about demographics, attendance, discipline and performance on standardized tests.

And for the first time, the reports publicize each school’s mobility rate — the proportion of students who enter and withdraw throughout the year — raising perennial questions about whether schools are funded fairly.

Across the city, schools lost 11 percent of their students during the school year and gained 9 percent for a net enrollment loss of 2 percent. But the citywide figure masks huge variation.

Many neighborhood schools like Anacostia, which are legally bound to take all comers, see double-digit turnover and an overall increase in the number of students they serve. But other schools — including neighborhood schools in affluent areas, application-only high schools and high-performing charter schools — tend to be far more stable.

Many lose students but add very few or no new students throughout the year, often because they aren’t required to accept new students.

Thurgood Marshall Academy, for example — a highly ranked charter high school a mile from Anacostia High — lost 7 percent of its students mid-year and gained none. Another highly regarded charter, Two Rivers, gained no students and lost 1 percent.

Eighty percent of schools in the traditional system see a net gain in enrollment; 90 percent of charter schools see a net loss.

Pete Weber, chief of data and strategy for the traditional school system, said officials are working to understand why students leave and where they go, and he added that publishing the numbers is an important first step toward making a difference.

“The fact that DCPS and charter schools are working together is a big deal,” Weber said. “I don’t know of other jurisdictions where the two sectors have worked together as effectively.”

The data come after years of complaints about “churn” from advocates for traditional schools, who have accused charters of pushing out very difficult children.

Scott Pearson, executive director of the D.C. Public Charter School Board, said that although there are many valid reasons for a student withdrawing mid-year, he would like to see less mobility among charters. He said that the effort to make data public is meant to nudge schools to change without resorting to new regulations.

The city also must fix school funding, Pearson said. Currently, the traditional school system is funded based on its projected enrollment, and the projections tend to be high, to the perennial frustration of charter school advocates.

Charter schools receive money based on the number of students in seats on Oct. 5. The schools aren’t penalized for losing a student mid-year, but they also don’t get additional dollars if they take a new student mid-year.

“That’s probably creating the wrong set of incentives,” Pearson said, adding that he’d like to see both kinds of schools “paid based on who is actually at the school over time.”

The report is available online as a PDF. The D.C. Public Charter School Board also has posted the underlying raw data on its Web site.