D.C. Mayor Muriel Bowser, left, and D.C. Public Schools Chancellor Antwan Wilson discuss the findings from the final independent auditor's examination regarding districtwide policies on attendance and graduation in District Schools during a press conference at city hall on Monday. (Jahi Chikwendiu/The Washington Post)

One of every three graduates from the District’s public schools last year missed too many classes or improperly took make-up classes, undermining the validity of hundreds of diplomas, according to a report released Monday.

The study, commissioned by the Office of the State Superintendent of Education, takes the district’s central office to task and is the latest bolt of bad news for a school system reeling from a graduation scandal.

The analysis concluded the District’s schools are plagued by a culture that encourages educators to hand out diplomas to meet lofty graduation goals, even if that means giving a high school degree to a student who missed half of the academic year.

“This is indeed tough news to deliver, but very necessary to right the ship,” Mayor Muriel E. Bowser (D) said at a Monday news conference announcing the results of the investigation.

School system leaders also announced Monday that a fourth high-ranking official had been removed — the principal of Dunbar High School.

D.C. Public Schools — widely lauded for education retooling and seemingly rapid improvements — has been engulfed in a graduation controversy since November, when allegations emerged that Ballou High School in Southeast Washington improperly graduated students. Bowser ordered investigations into citywide graduation practices and discovered that chronic absenteeism is rampant across the nation’s capital and that teachers aren’t failing students when they should.

The final superintendent’s report released Monday — a preliminary review was issued two weeks ago — found that attendance policies are “rarely followed” and that most high schools violated credit recovery program requirements. In credit recovery, students are allowed to retake a class they failed, but the report found students racked up excessive absences in these recovery courses, and were sometimes improperly enrolled.

“At most [D.C.] high schools, students have been allowed to pass courses despite excessive unexcused absences, at times missing the majority of the course,” the report concluded. “Grade reductions and failures due to absences are rarely enforced by [D.C.] school teachers or administrators.”

The Office of the State Superintendent teamed up with the consulting firm Alvarez and Marsal to conduct the investigation.

At Anacostia High School in Southeast Washington, nearly 70 percent of the 106 graduates last year received their diplomas despite violating some aspect of city policy — the worst violation rate among comprehensive schools in the city. At Ballou, the school whose mispractices spurred the investigation, 63 percent of graduates missed more classes than typically allowed, or inappropriately completed credit recovery, according to the report.

One of the most damning findings came from Dunbar High School in Northwest Washington. Teacher-centered attendance records at the school were modified from absent to present more than 4,000 times for the senior class, which numbered fewer than 200.

Dunbar’s principal, Abdullah Zaki, was removed from the school in the wake of the findings. Zaki, who was named D.C. Public Schools’ principal of the year in 2013, referred a request for comment to the school system’s press secretary, who declined further comment.

“They have far more changes than any other school did,” D.C. State Superintendent of Education Hanseul Kang said. “They have been identified as an outlier.”

Earlier this month, the principal and an assistant principal at Ballou were removed from their posts. The chief of D.C. secondary schools has been placed on administrative leave — the highest-ranking official to be relieved so far.

The report was sharply critical in assessing shortcomings at the central office.

“A lack of support and oversight from . . . central office contributed significantly to policy violations system-wide related to grading, credit recovery, excessive absences and graduation of ineligible students,” the report found. “Specifically, training, communication, tools and monitoring were inadequate.”

Chancellor Antwan Wilson, who became leader of the District’s schools last February, released a separate report that focused on reforms needed to ensure those who graduate truly earn their diplomas.

He promised the system will improve grading and credit recovery policies, and provide training for principals, teachers, students and parents so they are aware of city rules. D.C. Public Schools’ central office will also view transcripts before graduation to confirm they are not in violation of city policy. By 2022, the school system will require citywide end-of-course exams to assess whether students mastered material during the academic year.

Wilson said the more stringent adherence to attendance and credit policies will be in effect for the class of 2018.

“Are you telling me that they didn’t know they were supposed to go to school?” Wilson said at the Monday news conference. “They know that they are supposed to go to school. You can have an attendance issue and not miss 30 periods of a class.”

The scandal threatens to undermine the legacies of high-profile changes enacted by former chancellor Michelle Rhee and her successor, Kaya Henderson.

Bowser declined to say whether Henderson was interviewed as a part of the investigation.

Henderson did not immediately reply Monday to a request for comment.

“I can’t speak for Chancellor Henderson,” Bowser said.

The investigation was prompted by a November article by WAMU and NPR that said Ballou High gave diplomas to seniors who did not meet graduation requirements. While the article focused on Ballou, the report from the state superintendent’s office examined attendance and grading practices across the city, determining that truancy is more severe at neighborhood schools such as Ballou than in charter or application schools.

Benjamin Banneker and School without Walls, two magnet high schools, were the only two schools that didn’t graduate any seniors in violation of city policy.