After months of FOIA requests and general nagging, the Office of the State Superintendent of Education has finally released data that appear to show rates of suspicious DC CAS answer sheet erasures continuing to decline in 2011.

An analysis of 2011 reading, math, science and biology exams by their publisher, CTB/McGraw-Hill, shows that 128 classrooms in public and public charter schools in the District had high rates of wrong-to-right erasures.

That’s a drop of nearly 50 percent from 253 classrooms in 2009. The 128 classrooms represent less than 3 percent of the total number of classrooms in which students were tested.

Elevated erasure rates are widely regarded as possible evidence that teachers have tampered with tests or given improper assistance to students. The 2011 numbers continue a trend in which the decline in suspicious erasures--which officials credit to improved security--has been accompanied by flat or falling test scores.

OSSE’s nine-page version of CTB/McGraw-Hill’s report--completed in July but slipped under the tree by agency elves this week during the holidays--does not break down the data by school, only by citywide grade level. So if there are specific schools that remain hot spots of cheating, they remain unknown to parents and public. After a series of e-mail exchanges, Tamara Reavis, OSSE’s director of assessments and accountability, placed the number of public and public charter schools involved at 54.

The information is clearly available. The report refers to an omitted Excel file that lists each school and the teacher in each “flagged” classroom.

OSSE said it is holding back on naming the schools until a new outside contractor studies the classrooms in question under an expanded set of criteria that go beyond elevated erasures to include classroom patterns and performance on past tests.

Erasures “are only one data point to flag classrooms,” Reavis said in an e-mail. “Wrong to right erasures alone do not indicate improprieties.”

DCPS has retained the test security firm Caveon for the last couple of years to investigate high-erasure classrooms. The firm’s work led D.C. Superintendent Hosanna Mahaley to invalidate 2010 test scores last May in three classrooms (at Noyes, C.W. Harris and Leckie elementary schools). But Caveon founder John Fremer said that Chancellor Kaya Henderson never asked the company to use all the forensic tools at its disposal.

OSSE’s effort would be the first citywide attempt (covering both public and public charter schools) to have an independent contractor probe suspect classrooms.

The District released an RFP (request for proposal) on Dec. 23 soliciting interest from outside firms. But given the poky nature of the city’s procurement process and the District’s interest in keeping the whole issue of cheating on the margins of public discussion, it could be a year before such a study is completed and released.

The 2011 data released this week show the highest concentration of high-erasure classrooms in the third grade, where 21 of 303 rooms (6.9 percent) were flagged in math tests and 6.3 percent in reading exams. Why erasure rates are highest in the third grade is not clear.

Evidence of cheating has clouded the city’s standardized testing program since 2009, when the The Post reported that then-D.C. State Superintendent Deborah Gist asked schools to investigate instances of outsized gains on the 2008 DC CAS.

A USA Today investigation published in March found that classrooms in more than 100 D.C. public schools showed higher-than-average rates of erasures from wrong to right answers on the annual tests between 2006 and 2010 (It did not include public charter schools in its analysis). D.C. Inspector General Charles Willoughby, assisted by the U.S. Department of Education, is investigating the newspaper’s findings.