NASHVILLE (AP) - Questions about grades being changed at a privately run online school are a good example of why the so-called virtual schools should be run by the government, a state lawmaker said Tuesday.

Democratic Rep. Mike Stewart of Nashville has proposed banning privately run virtual schools. His measure was to be introduced as questions were arising about grade-fixing at the Tennessee Virtual Academy, a privately run school.

In a Dec. 13 email obtained by WTVF-TV, the vice principal of the academy noted high numbers of failing grades in September and October and directed middle school teachers to delete them.

"After ... looking at so many failing grades, we need to make some changes before the holidays," according to the email the television station received from an anonymous source.

Academy officials didn't deny the email. They said they were modifying internal grading procedures, not fixing grades.

"Consistent wi th our school's unique mastery-based learning model, this modification was designed to help increase student engagement by rewarding students who made an extra effort to master the material and improve their scores," the school said on its website.

"Our decision did not impact the integrity of our grading system and had no relationship to any state tests."

K12 Inc., the nation's largest publicly traded online education company, runs the academy for Union County public schools.

Under a law passed in 2011 by the Republican-controlled General Assembly, the academy began operations in the 2011-2012 school year, enrolling nearly 1,800 K-8 students from across the state. State payments to K12 are a little over $5,000 per pupil.

State officials have been questioning the K12 operation. Education Commissioner Kevin Huffman called its first-year test results "unacceptable."

State figures showed the academy fell into the bottom 11 percent of schools for stu dent gains, as measured under the state's value-added assessment system. The cyber school scored a 1 on the 5-point scale.

"K12 Inc. is attempting to game the system by apparently changing grades of its students to hide its ... failure," said Stewart, who is expected to present his bill at a House Education Subcommittee on Tuesday.

Another measure scheduled to be presented was Gov. Bill Haslam's proposal that would place stricter enrollment requirements on online schools established in Tennessee.

The bill would cap student enrollment at a virtual school at 5,000 students, and initial enrollment would be limited to 1,500, depending on the school's performance.