D.C. Schools Chancellor Kaya Henderson said Tuesday that allegations that school employees tampered with standardized tests between 2008 and 2010 are “fictitious” and pointed to a series of investigations that have yielded no evidence of large-scale cheating.

“There is no widespread cheating at DCPS,” Henderson said in a statement released Tuesday, responding to renewed attention to the cheating allegations this week. “Our teachers work hard every single day in our classrooms, and deserve credit and support, not unwarranted suspicions and doubt.”

D.C. schools officials released Henderson’s statement one day after news reports about a recently unsealed whistleblower complaint filed in 2011, in which former Noyes Education Campus principal Adell Cothorne outlined numerous allegations.

Cothorne alleges that one evening in 2010, shortly after the administration of a midyear practice exam at Noyes, she stumbled upon three staff members in a school office, surrounded by hundreds of test booklets and erasers.

Cothorne says she reported the incident to two central-office administrators, neither of whom took action.

Henderson disputed that account. “Ms. Cothorne claims to have reported this to DCPS. We have no record of this report,” the chancellor’s statement said. “Staff close to the school and staff named in her complaint have no record of these alleged conversations.”

D.C. schools have been scrutinized for their unusually high number of wrong-to-right erasures on the D.C. Comprehensive Assessment System — the annual exam that measures student performance and is used to determine which teachers and principals receive cash bonuses.

Cothorne says that because of the after-hours encounter with the three staff members, she tightened security for the end-of-year exam, and that test scores dropped more than 25 percentage points from the year before. She tells her story in a “Frontline” television documentary that was scheduled to air at 10 p.m. Tuesday.

Cothorne’s attorney said she would comment for this story but had not done so as of late Tuesday. Reached late Tuesday, Cothorne said she had not yet seen the “Frontline” episode and declined to comment.

Henderson said the former principal never mentioned the allegations when she was interviewed twice by an independent investigator.

“Even when asked if there was anything else she wanted to bring up to these independent investigators, she also didn’t identify any testing problems,” Henderson said in the statement.

Cothorne’s allegations of “systemic” cheating at Noyes triggered a U.S. Education Department investigation. Officials with the inspector general’s office at the Education Department said Monday that they had concluded their work and did not identify widespread cheating.

The federal investigators worked in tandem with the D.C. inspector general, who investigated Noyes for 17 months before concluding in August that there were isolated test-security problems but no rampant cheating at the school. Cothorne has said she was not interviewed as part of that probe.

Henderson said in the statement that investigators had found one incident of cheating at Noyes and said an employee was terminated as a result.

Henderson questioned Cothorne’s motivation for filing the whistleblower complaint; the former principal sought a percentage of funds recovered by the federal government had the case gone to trial, according to court documents.

“The fact that she has decided to attempt to personally profit financially through fictitious claims, rather than improve educational opportunities for our students, is extremely disappointing,” Henderson said.