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

Two federal agencies and the D.C. Office of the Inspector General are investigating the District’s public school system following revelations of inflated graduation rates, according to a current and a former D.C. government employee with direct knowledge of the probe.

The nature of the inquiry is unclear, but the probe is focused on Ballou High School, where allegations were first raised about diplomas wrongly awarded to chronically truant students. The federal agencies involved are the FBI and the U.S. Department of Education Inspector General’s Office. Those agencies and the D.C. Inspector General’s Office declined to comment and would not confirm or deny the existence of an investigation.

A spokeswoman for D.C. Public Schools also declined to comment.

The current and former District employees said investigators are reviewing what happened at Ballou last year, when more than half of the class graduated despite missing too much school — with some seniors racking up more than 100 absences.

In January, a school system attorney went to Ballou and met with educators who taught ­seniors during the 2016-2017 academic year and asked them to turn over documents as part of a “federal investigation,” according to government employees familiar with the visit. The attorney asked the teachers to hand over paper documentation they still had from students, including sign-in sheets, notes on parent-teacher conferences or behavior incidents.

The existence of an investigation adds another dimension to a scandal that has engulfed the school system since November, when allegations arose that Ballou permitted students to graduate even when they barely showed up to school.

Records shared with The Washington Post by a former schools employee showed that some students missed more than 100 days of school but still received diplomas and that other students were allowed to take makeup classes in violation of district policy. Emails shared with The Post showed that the Ballou principal instructed teachers to improperly input grades. The principal did not respond to inquiries about grading.

The Education Department’s Office of the Inspector General is the law enforcement arm of the federal agency, investigating subjects such as fraud in schools and in student loans. The office also conducts audits and has in recent years found that two states — Alabama and California — inflated graduation rates.

The scandal imperils the legacy of school reform begun by former D.C. schools chancellor Michelle Rhee, who instituted high expectations for test scores and graduation rates. She controversially tied the results to the job security and pay of teachers and principals, forging a system in which educators said they felt pressured to get results. That system was continued by her successor, Kaya Henderson, who aimed to lift graduation rates by 22 points in five years. Chancellor Antwan Wilson, who started in the school system a year ago, laid similarly ambitious plans.

Mayor Muriel E. Bowser (D) ordered an investigation into absenteeism in the school system. On Monday, the Office of the State Superintendent of Education published a damning report showing that one-third of D.C. public school graduates last year improperly received diplomas, exposing a “culture of passing” that prized glowing statistics over adhering to school system policies. School leaders said in the report it would be impossible to meet the District’s ambitious graduation targets without breaking the rules.

Investigators who prepared the report found widespread policy violations in several schools, including giving diplomas to students who had not taken all required courses and to students who had missed so much class they should have failed. At Dunbar High, investigators found that attendance records had been changed 4,000 times from absent to present in a senior class of fewer than 200.

Henderson, the former chancellor, was not interviewed by the state superintendent’s office as part of the investigation, according to that office. A representative of Henderson said this week the former chancellor was out of the country and could not be reached for comment.

WJLA-TV first reported the involvement of the FBI, the U.S. Department of Education and the D.C. Office of the Inspector General last month.

In the aftermath of the revelations, the district removed four school leaders, including the Ballou and Dunbar principals, the assistant principal at Ballou and the secondary schools chief.

It is not the first time a school system has made such discoveries, but the scandals rarely attract the attention of law enforcement. One case stands apart: In Atlanta, several school officials were convicted in 2015 of participating in a conspiracy to inflate test scores that involved at least 200 educators and 40 schools. Some received prison sentences.