The U.S. Department of Education has joined the District’s investigation into allegations that some recent big gains on standardized test scores might have been the result of cheating by teachers or principals, a D.C. official said Thursday.

Roger Burke, a spokesman for D.C. Inspector General Charles J. Willoughby, said investigators from the Education Department’s Office of Inspector General have been active in the probe, which was requested in March by Schools Chancellor Kaya Henderson.

Burke said he was not aware of the department’s participation before Thursday and did not know how long it had been playing a role or whether its help had been requested by the District. Beyond that, he refused to elaborate.

“I’ve gone further than I usually do,” he said.

Catherine Grant, a spokeswoman for Education Department Inspector General Kathleen Tighe, declined to comment.

“Per our policy, we do not confirm or deny investigative activity,” she said.

Henderson, who will join Mayor Vincent C. Gray (D) on Friday in announcing the District’s 2011 test scores, said she was not aware of the department’s participation, but she expressed no displeasure.

“I welcome the most thorough investigation possible,” she said.

The department’s involvement comes amid heightened concern about cheating on tests the government uses to determine whether schools have met progress benchmarks under the No Child Left Behind law. Test scores have also been increasingly employed as a measure of teacher effectiveness and a make-or-break factor in career trajectories of principals and other administrators.

USA Today reported in March that from 2008 to 2010, classrooms in more than 100 D.C. schools registered unusually high rates of erasures on answer sheets; wrong answers were changed to correct ones. A test-security firm the District hired to investigate found evidence of “testing irregularities” at three schools during administration of the 2010 D.C. Comprehensive Assessment System exams. As a result, D.C. officials invalidated test results in three classrooms at Noyes Education Campus and Leckie and C.W. Harris elementary schools and, according to multiple school system and union sources, dismissed at least two teachers.

Henderson said she was satisfied that the security firm, Caveon, did a thorough job but nevertheless requested the follow-up inquiry by Willoughby’s office.

This week, Georgia officials released the results of an investigation into Atlanta public schools, which found that 178 teachers and principals in 44 schools cheated on the 2009 state test, either by giving inappropriate help to students or altering answer sheets. The probe concluded that top school officials, including then-Superintendent Beverly Hall, knew about evidence of cheating and either ignored it or tried to cover it up.

Investigators said “a culture of fear and a conspiracy of silence” in Atlanta schools fed the misconduct.

Some D.C. observers said the Atlanta probe, ordered in 2010 by then-Gov. Sonny Perdue (R) after he declared a local investigation “woefully inadequate,” should be a model for the District. The Georgia inquiry was headed by two former district attorneys and staffed by nearly 60 agents and other personnel of the Georgia Bureau of Investigation. Investigators had subpoena power to compel testimony and offer immunity from prosecution to those who cooperated. According to the 800-page report, they conducted more than 2,100 interviews and reviewed more than 800,000 documents.

By contrast, the District’s inquiry has been much smaller in scope. Burke would not disclose how many investigators are assigned, but he said the office has conducted 10 interviews, with at least eight more scheduled. He added that investigators have been slowed because of the summer break.

“Our disadvantage was that it was the end of the school year when this came up,” Burke said.

Burke said that while the office does have administrative subpoena power, it has not been used in the five years he has worked for the agency.