School Without Walls High is one of the District’s most competitive application schools. (Nikki Kahn/The Washington Post)

More than 200 D.C. families that thought their children would have a shot at getting into one of the city’s most prestigious public high schools had their hopes extinguished last week when they learned they no longer qualify — because of a school system blunder.

D.C. education officials acknowledged that they failed to follow city rules when trying to expand access to School Without Walls High School, a misstep that could result in fewer students from low-income families applying.

In a letter to 226 families, John O. Stover III, interim chief of secondary schools at D.C. Public Schools, wrote that the school system “did not adhere to specific regulatory requirements for publishing changes to admission criteria.”

“We want to express our sincerest apologies for the misinformation surrounding any changes to the admissions criteria for SY19-20,” Stover wrote.

The school system says it will delay for a year its effort to expand access to School Without Walls.

The 600-student school in Northwest Washington educates the lowest percentage of at-risk students of any high school in the traditional public school system. At-risk students are defined as those whose families are homeless or who receive food stamps or public financial support, or those who are a year or more behind in high school.

Just 12 percent of students at Walls are considered at-risk, vs. 46 percent in public high schools citywide, according to city data.

Each winter, hundreds of children in the District who have at least a 3.0 grade-point average qualify to take the admission test at School Without Walls.

This year, school officials said that prospective students also needed to earn passing marks on a national standardized exam to qualify to take the admission test.

But because black and Hispanic students from low-income families tend to score lower on the standardized test than their white and wealthier peers, school officials also quietly rolled out a pilot program that would have enabled all students ranked in the top 15 of their middle schools to take the Walls admission test — even if they did not pass the national standardized exam.

That strategy could have enabled Walls to capture students from every middle school in the city, including those with high concentrations of students from low-income families. At some middle schools, just 1 percent of students pass the standardized exam.

The 226 families whose students hoped to get into Walls but received the letter from the school official probably failed to score high enough on the standardized test while hitting other marks.

School leaders told parents at events and enrollment fairs in the fall about the pilot program, but, in a violation of city rules, never documented the changes in published materials or on the DCPS website that explains the lottery that is used by families hoping to obtain seats in schools outside their neighborhoods.

“I can’t promise the families of [D.C. Public Schools] that we will never make mistakes, but I can promise you that when we do, we will tell the community and work quickly to fix the situation,” Deputy Mayor for Education Paul Kihn said in a statement. “As soon as we discovered the mistake related to the School Without Walls admission process, we acted quickly to communicate with students and families; still, though, I regret any disappointment we may have caused.”

The effort to diversify the top schools that admit students by application is not limited to the District. Last year, New York City Mayor Bill de Blasio announced a plan to diversify some of that city’s application high schools by phasing out an admission test and awarding slots to top middle school students from throughout the city.

The plan had supporters but also drew intense backlash. Asian American civil rights groups and parents sued New York City officials, alleging that the plan amounts to unconstitutional discrimination against Asian American students, who occupy more than half of all seats at the eight schools that use testing for admissions.

D.C. schools spokesman Shayne Wells said one objective of the pilot program at School Without Walls was to determine whether having more students take the admission test would produce a student body that was more socioeconomically diverse — or whether the admission test would still be a barrier. The admission test is untimed and has a writing component.

In most years, more students pass the Walls admission test than can be accommodated at the school, so the citywide lottery makes the final decision on who gets to enroll.

Results from the standardized tests show why officials sought to expand the potential pool of students. Citywide, 18 percent of black students at traditional public and charter schools in 2017 passed the math portion of the national standardized test, and 22 percent passed the English section.

That compared with 76 percent of white students who passed the math portion and 82 percent who passed the English section. And 26 percent of Hispanic students earned passing marks on the math portion, while 29 percent passed the English portion.

The Walls student body is disproportionately white. Systemwide, 14 percent of D.C. students are white. At Walls, 43 percent of students are white, 31 percent black, 13 percent Hispanic, 8 percent Asian and 5 percent identify as two or more races.

Markus Batchelor, the Ward 8 representative on the D.C. State Board of Education, said there are constant conversations in the city about increasing the representation of low-income students in selective schools.

Banneker High, another sought-after application school, does not require an admission test, though students have to pass the national standardized exam to be considered for enrollment.

Banneker’s student body is nearly entirely black and Hispanic, but its at-risk population is 20 percent, well below the city average.

The school system is partnering with Bard College to open an application high school next academic year that would allow students to graduate with a two-year college associate degree. The school will be east of the Anacostia River — a large swath of the city with some of the highest concentrations of poverty.

“Figuring out creative ways to expand access to selective seats and other specialty programs is something I’d be interested in exploring,” Batchelor said. “If there’s going to be an implementation of something like this, I would be interested in seeing the results.”