A massive scandal involving teachers and administrators changing answers on standardized tests in Atlanta public schools has led to arrests and indictments, but a smaller cheating scandal in D.C. public schools has largely been brushed aside as being limited and relatively inconsequential. That could soon change.

Education reporter John Merrow, who recently produced an hour-long documentary for PBS’s Frontline on former D.C. Schools Chanceller Michelle Rhee, wrote on his blog yesterday that a confidential memo he gained access to shows that the cheating scandal that seemed limited in scope may have been larger than once thought, and that Rhee may have failed to properly investigate:

Michelle A. Rhee, America’s most famous school reformer, was fully aware of the extent of the problem when she glossed over what appeared to be widespread cheating during her first year as Schools Chancellor in Washington, DC. A long-buried confidential memo from her outside data consultant suggests that the problem was far more serious than kids copying off other kids’ answer sheets. (“191 teachers representing 70 schools”). Twice in just four pages the consultant suggests that Rhee’s own principals, some of whom she had hired, may have been responsible (“Could the erasures in some cases have been done by someone other than the students and the teachers?”).

In March 2011, USA Today reported that from 2006 to 2010, the Crosby S. Noyes Education Campus in Northeast D.C. and various other schools saw dramatic jumps in scores on citywide standardized tests. But according to documents it got from the school system, tests given to students there and at other schools showed abnormally high erasure rates, raising the prospect that teachers and administrators were correcting wrong answers in hopes of producing higher test scores.

Despite claims by some former administrators that cheating was more widespread, investigations by the D.C. Inspector General and Department of Education said it was relatively limited, seemingly sparing Rhee and now-Chancellor Kaya Henderson from the type of pressure (and consequences) seen recently in Atlanta.

But according to the newly uncovered memo—which USA Today also got a hold of—cheating dating back to 2008 may well involve many more teachers, administrators and schools than originally thought. Additionally, Rhee didn’t do enough to investigate it at the time. Explains Merrow of the memo, which was kept confidential but allegedly discussed by Rhee and Henderson:

The gist of his message: the many ‘wrong to right’ erasures on the students’ answer sheets suggested widespread cheating by adults.

“It is common knowledge in the high-stakes testing community that one of the easiest ways for teachers to artificially inflate student test scores is to erase student wrong responses to multiple choice questions and recode them as correct,” Sanford wrote.

Sanford analyzed the evidence from one school, Aiton, whose scores had jumped by 29 percentiles in reading and 43 percentiles in math and whose staff-from the principal down to the custodians-Rhee had rewarded with $276,265 in bonuses. Answer sheets revealed an average of 5.7 WTR erasures in reading and 6.8 in math, significantly above the district average of 1.7 and 2.3.

DCPS spokeswoman Melissa Salmanowitz said that there’s really nothing new to what Merrow is reporting, and that the issue has already been looked into.

“This document is not new information. Previous documents have confirmed what Sanford’s document indicates—that DCPS did not have information at that time to complete an investigation and that OSSE’s flagging methodology was incorrect,” she said. “The only smoking gun here is that Sanford cautioned DCPS from coming to any conclusion when he wrote that much of what was known was based on incomplete information.”

“Chancellor Henderson has no recollection of receiving/reading this document, nor of discussing it with then-Chancellor Rhee. At the time, she managed Human Capital and would not likely have been involved in erasure analysis work. We remain confident in the results of every investigation conducted to date all of which have concluded that there is no widespread cheating at DCPS.”

In early February Councilmember David Catania (I-At Large), who chairs the D.C. Council’s Education Committee, introduced a bill that would make cheating on standardized tests illegal.