Officials from Bill Thompson’s campaign are pointing to a story about grade tampering at a Bronx high school as evidence that the city’s education data is unsound.

Yesterday, I reported that current and former teachers at Herbert Lehman High School are accusing principal Janet Saraceno of transforming the school into a “diploma mill.” Student transcripts given to GothamSchools show that in the last year, dozens of students have been given credit for courses they failed or never took.

Mayor Bloomberg has staked his reelection on his claim that graduation rates are rising, an assertion Thompson  questioned in an audit he released as comptroller.

“Today’s article about Lehman High School grading fraud is another appalling example of Mike Bloomberg’s corrupt Department of Education,” said Thompson campaign spokesman Mike Murphy. “This is the second story this month to prove that Bloomberg has greatly exaggerated the success of his Department of Education by padding, manipulating and falsifying statistics, including graduation rates and test scores.”

Christopher Cerf, an education policy adviser for the Bloomberg campaign, defended the mayor’s accountability system, which rewards or punishes principals based on their schools’ test scores and graduation rates.

“We cannot comment on any aspects of this, but we certainly do not condone the kinds of things that are alleged. But at the same time, we believe that accountability for student outcomes is a central driver of positive reform and we believe it is critical to hold everybody in the system accountable for student results.”