Two Tennessee school systems, including the state’s largest district, are being audited by the Tennessee Department of Education for potential cheating on their 2013-14 state achievement tests, state officials confirmed on Tuesday.

The state is investigating TCAP results at Alcy and LaRose elementary schools in Shelby County, as well as Robertson County Schools. It already has completed an audit of Williamson County Schools, where investigators found no evidence of a security breach.

The districts were flagged after the state did an erasure analysis, which analyzes the percent of answers changed from wrong to right on the multiple-choice exam. Officials hired psychometricians to examine the three districts where small groups of students had frequently changed answers.

Department of Education spokeswoman Ashley Ball cautioned that the audit doesn’t mean the entire district had a high rate of erasure.

Though state officials have been analyzing erasure marks since the 2011-2012 tests, this was the first time they shared the results with districts, in an effort to help administrators examine their testing security protocols.

Shelby County Schools already has undergone an internal investigation and found no evidence of cheating, said district spokesman Christian Ross.

“We did not find anything indicating that testing had been handled inappropriately,” district officials said in a statement released Wednesday. “The state department is also conducting its own investigation, and we are still awaiting those results.”

Parents were not alerted because the district was following protocol provided by the state and is waiting until the state finishes its investigation, according to the statement.

The statement also explained how assessments are handled after testing. The test administrator distributes and collects the tests in the presence of a proctor. While not in use, all materials are secured in a locked location to which only the principal and the building test coordinator have a key.

Once test results are received, the district reviews the scores to determine whether a school needs further review.

Beginning next school year, Tennessee students no longer will take tests that are entirely multiple choice. The new TNReady assessment, which will be mostly online, incorporates open-ended questions in addition to traditional multiple-choice test items.

Editor’s note: This story has been updated to include a response on Wednesday from district leaders in Shelby County.