This post has been updated.

(Correction: Coolidge High School and Houston Elementary were incorrectly listed as schools where pass rates declined in reading and math on the 2010 DC CAS after being flagged for suspicious erasures on the 2009 test. Coolidge gained in both reading and math in 2010. Houston improved in math.)

There’s no way to know with certainty. But 24 of the 41 DCPS schools that had classrooms flagged by D.C. officials for high rates of wrong-to-right erasures on the 2010 DC CAS saw reading and math pass rates drop in 2011, new test data shows. Another 10 dropped in at least one category.

As my colleagues Nick Anderson and Jay Mathews reported last week, among the biggest losers were J.O. Wilson Elementary and the Noyes Education Campus. The latter was the focus of a USA Today investigation published in March raising questions about test score gains across the District. After 16 of Noyes’s 20 classrooms registered high levels of erasures in 2010, officials promised heightened test security. This year’s pass rate in reading dropped more than 25 percentage points, to 32 percent. The pass rate in math dropped more than 20 points, to 28 percent.

At J.O. Wilson, where all 10 testing classrooms were flagged in 2010, the percentage of students reading at the “proficient” level or above dropped from 66.7 to 53.4 percent. In math, the figure went from 75.7 to 53.4 percent. Other schools that posted declines in 2011 after having multiple classrooms flagged in 2010 include Ludlow-Taylor, Leckie and Martin Luther King elementaries and the Whittier Education Campus.

Correlation, to be sure, doesn’t prove cause and effect. Erasures are only a marker for possible cheating. Forty-two DCPS schools lost ground in both math and reading this year. And a handful of high-erasure schools scored gains in pass rates this year. The matter is under investigation by the D.C. and U.S. Department of Education inspectors general.

But the same pattern played out in 2010, as well. Eight of the top 10 high-erasure schools in 2009 posted significant declines in reading and math on the 2010 tests. These were J.O. Wilson and Noyes (again) along with Barnard, Plummer, Houston, Hendley, Burrville and Harris elementary schools, the Marie Reed Education Campus and Coolidge High School (Birney was found to have high erasures in 2009 but was closed for low enrollment).

School officials say they have refined and improved test security each year since the erasure issue first surfaced in 2009. If you take them at their word, then the numbers show that erasures (and possible cheating) declined as protocols tightened.

According to the numbers unearthed by USA Today, 380 classrooms across 96 schools had high erasure rates in 2008. Of those 96 schools, nine had between 75 and 99 percent of their classrooms under suspicion. Thirteen schools showed between 50 and 74 percent of classrooms with unusual erasure levels.

In 2009, those numbers dropped significantly, to 165 classrooms across 46 schools. Just four schools had between 75 and 99 percent of their rooms flagged. In 2010, the downward movement continued: 110 classrooms in 41 schools.

We expect to get the 2011 erasure data within the next few weeks.