A D.C. government education agency is seeking an outside firm to investigate the city’s 2011 standardized test scores.

Officials said the probe will be part of a strengthened set of procedures to ensure the validity of results on the annual D.C. Comprehensive Assessment System. Scores from previous years have come under scrutiny. In May, the District invalidated some 2010 results at three schools after an investigation found evidence of or reasons for a strong suspicion of cheating.

“Testing impropriety is an issue this agency takes very seriously,” State Superintendent of Education Hosanna Mahaley said in a statement Friday. “Any violation of security undermines trust and faith in our entire educational system by casting doubt on the positive growth we have begun to see citywide.”

The outside firm will review individual classroom results that have been flagged for scrutiny, based on a new set of measures education officials developed to improve test validity, Mahaley spokesman Marc Caposino said Saturday. The measures include monitoring for surprising jumps in performance, unusually uniform classroom performance on tests, and high numbers of answers that have been erased and changed from wrong to right.

The District has sought similar outside help to review test results in the past. Utah-based Caveon Test Security examined classroom-level results in 2009 and 2010. The company identified no testing irregularities in 2009 but found signs of cheating in three classrooms in 2010, leading to the invalidation of those scores.

Mahaley’s agency is in charge of numerous programs that support the public school system and public charter schools and ensure compliance with federal education laws.

D.C. Schools Chancellor Kaya Henderson, who runs the 46,000-student school system, also asked the D.C. inspector general to investigate allegations of possible cheating after a USA Today report in March found classrooms in more than 100 D.C. public schools had higher-than-average rates of wrong-to-right erasure marks on test answer sheets.

The U.S. Education Department is assisting the inspector general.

In the past year, evidence or allegations of cheating in several cities have raised questions about the reliability of high-stakes tests and threatened to undermine education reform efforts. A state-led investigation in Georgia found that 178 teachers and principals in 44 Atlanta schools tampered with results from 2009 state tests.

U.S. Education Secretary Arne Duncan in June sent a letter to state schools chiefs urging them to step up efforts to “ensure the integrity of the data used to measure student achievement and ensure meaningful educational accountability.”

A group of national testing experts is advising the District on its security practices.

One member of the group, Rachel Quenemoen, a senior research fellow at the National Center on Educational Outcomes at the University of Minnesota, said such advisory committees work with state governments across the country. “In the last few years, many states have worried about test security, and all states are examining their protocols,” she said.