While LL was away, the city’s Office of Inspector General struck again.

The IG released a report on its investigation into allegations of cheating on standardized tests at D.C. public schools. The office began its investigation more than a year ago after a lengthy piece by USA Today in March 2011 questioned why so many tests of D.C. students had a higher-than-average number of questions changed from wrong to right. The paper focused heavily on Noyes Educational Campus, where the stunning rise in test scores coincided with extremely high average of wrong-to-right “erasure” marks on tests.

On the 2009 reading test, for example, seventh-graders in one Noyes classroom averaged 12.7 wrong-to-right erasures per student on answer sheets; the average for seventh-graders in all D.C. schools on that test was less than 1. The odds are better for winning the Powerball grand prize than having that many erasures by chance, according to statisticians consulted by USA TODAY.

The paper also found high that several other schools high wrong-to-right erasure rates. So what did the IG turn up after more than a year of investigating? Not much. The IG’s 14-page report says there’s “insufficient evidence on which to conclude” that there was widespread cheating in D.C. schools.

That may be the case, but it’s hard to take the IG’s word for it, as its report raises more questions than it answers.

The Washington Post’s Jay Mathew‘s also already put a good hurtin’ to the IG’s weak work, which includes limiting the investigation to Noyes (in part because School Chancellor Kaya Henderson suggested that), and not interviewing any students or experts on test erasure marks.

A spokeswoman for Inspector General Charles Willoughby says the office stands by its work and “the report speaks for itself.” As LL noted in a column last year, the District’s main watchdog has failed to inspire confidence for several years. Part of the complaints lawmakers have with Willoughby’s work is that it takes so long. In this latest report, the IG only interviewed 32 current or former Noyes staffers and 23 parents. USA Today noted last summer that some of the teachers had already been interviewed. Yet still the report wasn’t issued until last week. Why? In a footnote to the report, the IG’s office says that it “encountered delays” in its investigation because it was hard to schedule interviews that didn’t disrupt class schedule. Puh-leeeze. (The IG’s spokeswoman declined to discuss why the $15 million-a-year agency took so long to complete such a limited investigation.)

Then there’s the fact that there appears to have been little follow-up work to one teacher’s allegations that there was a well-coordinated attempt to cheat at Noyes. According to the teacher, whom the IG refers to only as “Teacher 1,” the school’s guidance counselor t0ld teachers to seat their students according to how they were likely to do on the test and put the kids who might score in the “proficient range” if given a little boost in the back of the classroom, where it would be harder for test monitors to see teachers giving them help. Teacher 1 said he or she would help students by looking over their shoulders and silently pointing to wrong answers until the students changed them to right answers. None of the other 15 teachers interviewed by the IG verified Teacher 1’s account about being ordered to seat students based on how they scored on the test.

It could be that Teacher 1 is lying; the IG says in a footnote that the teacher was fired because of his or her conduct, but doesn’t say when. But if this last year has taught D.C. anything, it’s that even a fired city employee with a vendetta can still tell the truth (come on down, Sulaimon Brown). Teacher 1 also says school officials distributed an advance copy of the test to teachers before test day. Teacher 1 says the guidance counselor gave the test to Teacher 1 and another teacher (Teacher 2) and said “to do what you need to do.” Both the guidance counselor and Teacher 2 say that’s not true. But another teacher (Teacher 3) says the guidance counselor did hand out advance copies, with instructions to go over the test with students (though not with explicit directions to “give students advance knowledge of the test questions,” according to the IG).

The IG says it has no reason to doubt Teacher 1’s veracity about his or her own conduct, but can’t corroborate the rest of the story because the other teachers and staff (who all have a huge incentive to not admit to any wrongdoing) contradict it. And then the IG just leaves it at that.

LL can’t help but wonder what a more aggressive investigative body faced with a similar roadblock might have done. In Georgia, where similar questions were raised about test cheating, an aggressive state probe conducted by some 50 investigators included 8,000 interviews and reviews of more than 800,000 documents. The result: nearly 200 educators were found to have cheated at 44 schools in Atlanta.