The Atlanta Journal-Constitution, whose investigative reporters revealed a massive cheating scandal in their city schools, has just released an investigation into test-score patterns in 49 states that can indicate a high likelihood of manipulated scores.
Charlotte-Mecklenburg Schools isn't on the list of districts flagged as questionable (see a map here, or look up individual districts here), based on "improbable clusters of unusual score changes." Several districts surrounding Charlotte, including Gaston, Iredell-Statesville, Hickory and South Carolina's York 4, pop up on the map -- in each of those cases, because one of the last four years showed test-score shifts "outside the norm," rather than a persistent pattern.
Cities that showed such extreme swings that they resemble the patterns that clued reporters in to the cheating in Atlanta are Baltimore, Dallas, Detroit, East St. Louis, Gary, Houston, Los Angeles and Mobile County, Ala.
As the Journal-Constitution article notes, the statistical analysis doesn't prove cheating. And as local skeptics are likely to add, a reasonable rating doesn't mean there's never been any monkey business, either.