The District has invalidated test results for three classrooms that participated in 2010 citywide exams after an investigation found evidence or a strong suspicion of cheating, officials announced Wednesday.

D.C. State Superintendent of Education Hosanna Mahaley did not specify the schools or classrooms involved, or the specific test security violations. But she said that “three proven incidents of cheating” in a school system with 3,800 classrooms and 45,000 students affirmed the effectiveness of security protocols for the D.C. Comprehensive Assessment System.

“Most of our teachers and students are playing by the rules,” Mahaley said.

Security on the high-stakes standardized tests has been called into question since a USA Today investigation published in March found that classrooms in some D.C. public schools with steep test score gains showed higher-than-average rates of erasures from wrong to right answers on the annual tests between 2008 and 2010.

Elevated erasure rates are regarded by testing experts as an indicator that students were improperly steered toward changing answers, or that answer sheets were tampered with after administration of the test. Acting Chancellor Kaya Henderson has asked the office of D.C. Inspector General Charles Willoughby to investigate.

It was not clear from Mahaley’s comments, which she made at Mayor Vincent C. Gray’s (D) weekly press briefing, whether the invalidations were the result of the inspector general’s ongoing probe, an internal D.C. school system inquiry, or her own agency’s probe.

District officials also released a list of test security incidents on the 2011 DC CAS, which was administered last month. The state superintendent’s office said it found 31 irregularities, of which 14 will be subject to further action by the District authorities.

Brief descriptions of the incidents include “inappropriate level of support given to students,” and “three teachers in three classrooms provided aid to students.”