This story has been updated.

The former principal of an award-winning D.C. public school has accused teachers and administrators of systematically cheating on standardized tests in order to win cash bonuses and a steak dinner, according to recently unsealed federal court documents.

Part of a complaint filed in May 2011, the allegations triggered an investigation by the U.S. Education Department’s office of the inspector general. That office said Monday that it had concluded its work and found no evidence of widespread cheating in D.C. schools between 2008 and 2010.

The announcement came one day before a scheduled broadcast of a “Frontline” television documentary in which Adell Cothorne, who was principal of Noyes Education Campus in 2010-11, describes some elements of her allegations. But the details in a whistleblower complaint Cothorne made against the D.C. government in 2011 are far more extensive and allege that cheating occurred at other schools as well.

“The falsification of DC CAS test scores is systemic, and the veracity of the testing process and DC CAS scores has been questioned by other DCPS principals,” the complaint says, referring to the D.C. Comprehensive Assessment System tests, which measure student performance and were used to determine teacher and administrator bonuses.

Cothorne’s complaint was filed under the False Claims Act on behalf of the federal government, and Cothorne sought a percentage of any potential financial proceeds had the case gone to trial.

The Education Department’s probe was the latest in a string of investigations into alleged cheating in D.C. schools, which had an unusually high number of wrong-to-right erasures on answer sheets between 2008 and 2010.

D.C. schools officials have maintained that widespread cheating did not occur in the city. Officials cite investigations by Caveon, a company that the school system retained to investigate those erasure rates, and by the D.C. inspector general’s office, both of which discovered only minor test-security problems.

“We are pleased that this report corroborates the findings of all other investigations - there is unequivocally no widespread cheating at DCPS,” D.C. Schools Chancellor Kaya Henderson said in a statement Tuesday morning.

“We hope this will finally put the issue to rest. Our teachers work hard every single day in our classrooms and deserve credit and support, not unwarranted suspicions and doubt.”

Cothorne’s attorney declined to comment.

The D.C. inspector general investigated Noyes for 17 months before concluding in August that no widespread cheating occurred there. The inspector general interviewed dozens of teachers and parents to reach that conclusion.

Education Department investigators worked with the D.C. inspector general, but federal officials focused on whether possible cheating meant city officials might have misrepresented the truth about test scores in their claims for payments from Race to the Top and other federal programs. Those programs provided millions of dollars to D.C. schools.

Federal investigators found only one instance of cheating that may have affected federal funding. That incident had already been reported by the D.C. inspector general, and the individual involved was fired. “Our investigation was unable to substantiate the allegations that false claims were made to [the Education Department] for payment of funds, and the U.S. Department of Justice declined to intervene,” the federal inspector general said in a statement Monday.

The lawsuit details the impressive test-score gains made under Cothorne’s predecessor, which resulted in cash bonuses of $10,000 to the principal and $8,000 to teachers in both 2008 and 2010.

After scores rose by more than 20 percentage points in 2007, former Chancellor Michelle A. Rhee allegedly challenged the principal to match those gains in 2008, according to the complaint. The reward was to be dinner for the staff at Ruth’s Chris Steakhouse.

In 2008 scores jumped again, and the Noyes staff was treated to dinner, according to the documents.

In her complaint, Cothorne says that shortly after she arrived at Noyes in 2010, a teacher pulled her aside and said: “You know, they cheat on their tests.”

Cothorne identifies three staff members she says she saw in November 2010, sitting in a room with hundreds of test booklets and erasers following the administration of a midyear practice exam, according to the complaint.

Cothorne also alleges that she reported what she saw to two central office administrators.

When Cothorne tightened security for the end-of-year standardized tests in 2011, students’ math and proficiency rates dropped more than 25 percentage points from the year before, she told “Frontline.”

The complaint alleges that other Noyes staff approached Cothorne and confirmed a “long history of cheating” at the school. The complaint also alleges that two other D.C. principals raised questions about test score gains at their schools.

Julie Tate contributed to this report.