A chalkboard in the lobby at Ballou High School. (Bonnie Jo Mount/Washington Post)

IN JUNE, 164 students graduated from Ballou High School. Just two months earlier, the assessment of officials at the Southeast Washington school was that only 57 students were on track to graduate; dozens of others were missing graduation or community service requirements or failing classes. How were these students able to graduate? Did they legitimately complete the required work? Or were they passed through and given diplomas they didn't deserve?

Those are the questions that must be addressed in the wake of a disturbing report that students who were ill-prepared or chronically absent were allowed to graduate after teachers felt pressure to pass them. According to an investigation by WAMU and NPR, a majority of Ballou's 2017 graduating class missed more than six weeks of school; one-fifth of the graduates missed over half the school year. D.C. school policy, put in place two years ago, dictates that a student fail a class after 30 absences. There are, however, provisions for students to get credit by showing proficiency in a subject or through credit recovery courses.

Mayor Muriel E. Bowser (D) and D.C. Public Schools Chancellor Antwan Wilson immediately announced there would be an investigation into Ballou and a separate inquiry into whether issues related to graduation and grading need to be addressed citywide. The D.C. Council will also hold an oversight hearing on the matter. These are welcome moves; it is important to know exactly what happened at Ballou.

It's also important to allow the investigations to run their course before drawing broad-based conclusions. Complicated issues are at play. For example, we were struck by the fact that among those interviewed were three former students of Ballou who are now in college, including one who was absent about half the school year. "If some of those kids end up finishing college who wouldn't have if they were not passed — isn't that the goal?" one reader tweeted.

Ballou is a historically troubled school serving some of the city's most disadvantaged students in one of the city's poorest neighborhoods. It has twice been reconstituted, and teacher turnover is a major issue. There have, though, been some signs of improvement, including a steady rise in test scores. The school received widespread praise, including from this page, after all of this year's graduating seniors applied and were accepted into college. Was that a sham? Mr. Wilson has said he believes the improvement to be genuine. In a Thursday appearance on "The Kojo Nmadi Show," he said some Ballou teachers told him that the school's hard-charging principal is the target of a vendetta by disgruntled employees.

"To be honest with you," Mr. Wilson said, "I don't know what mistakes were made at Ballou." It's time to find out and, if there was wrongdoing, make those responsible accountable.