TALLAHASSEE — State Education Commissioner Tony Bennett resigned Thursday, fueling controversy over the school grading system and delivering a blow to Gov. Rick Scott and the leaders working to overhaul Florida's system of school accountability.

Coming to Florida in January from Indiana, Bennett had faced mounting calls for his resignation this week after revelations that he intervened in the grading system in Indiana to benefit a charter school run by a prominent Republican Party donor.

On Thursday, Bennett said he was leaving his post immediately to avoid becoming a "distraction."

"The decision to resign is mine and mine alone, because I believe that when this discussion turns to an adult, we lose the discussion about making life better for children," Bennett said.

He called the news reports, first published by the Associated Press, "malicious and unfounded" and suggested information had been "leaked to the press" to damage him politically.

"I end my tenure with my head held very high, looking ahead, knowing that great things are ahead for this state under the leadership of Gov. Scott and the state Board of Education," he said.

Board Chairman Gary Chartrand recommended K-12 chancellor Pam Stewart serve as interim commissioner. The board will consider the proposal in an emergency conference call Friday.

Bennett's resignation comes at a particularly difficult time for the state Education Department, which is facing a narrow window to adopt new national standards known as the Common Core and the accompanying exams. The move has drawn intense opposition from tea party leaders who say standards should be determined at the local level.

At the same time, Florida's own school grading system has come under fire from superintendents, union leaders and parent groups — even as it is touted as a national model.

"The actions of former Commissioner Bennett in Indiana only served to further undermine the shaky trust Florida parents have in the school grading system here," said parent activist Colleen Wood, whose nonprofit organization 50th No More has called for a moratorium on letter grades for schools.

Stability has also been an issue. The Education Department has had three education commissioners and two interims during Scott's 31 months in office.

"We've got so many issues and items that need effective leadership and we've gone through a series of commissioners," Pinellas County superintendent Mike Grego said.

Bennett was recruited to Florida late last year to provide steady leadership after the abrupt resignation of former Commissioner Gerard Robinson.

He encountered some bumps in June, when superintendents leaned on him to institute a "safety net" to prevent school grades from crashing in light of new, more challenging state exams. Despite initial misgivings, Bennett ultimately conceded.

The exercise sparked a statewide dialogue that left some superintendents, parents and members of the state Education Board questioning whether school grades were valid or even necessary.

Shortly after, scathing emails published by the AP showed that Bennett had made changes to the school grading formula in Indiana after learning that a high-profile charter school would be awarded a C.

Bennett denied the changes, which boosted Christel House Academy's grade to an A, were motivated by politics.

"It is absurd that anyone would believe that I would change the grade of school based on a political donor or based on trying to hide a school from accountability," Bennett told reporters Tuesday. "What we did do is make sure we were getting a transparent policy right for Indiana schools and Indiana schoolchildren."

Bennett is a longtime ally of former Gov. Jeb Bush, whose Foundation for Florida's Future has driven education policy in Florida for the past decade. He is active in Bush's coalition of state education leaders, Chiefs for Change.

He said Scott urged him to stay in the position, but he resigned to keep the focus on education.

"I do not believe that Gov. Scott, as supportive and encouraging as he's been to me, . . . should have to spend his time if things do continue to trickle out," he said.

Bennett said he did not know what might "trickle out," and added that the emails had caught him by surprise.

Scott said little Thursday but released a statement praising Bennett's tenure.

State Senate Education Committee Chairman John Legg, however, said Bennett's departure was the right thing if it meant maintaining integrity for the state's accountability systems.

"We need to move forward to eliminate any question of improprieties," the Trinity Republican said, stressing he had heard no accusations that Bennett had acted inappropriately in Florida.

Hillsborough superintendent MaryEllen Elia called on the Board of Education to find a strong successor.

"What's important now is that Florida quickly establishes strong and stable leadership in the Department of Education," she said. "We have so much work to do, and this is a critical time for Florida's school accountability system."

Miami-Dade superintendent Alberto Carvalho, however, urged state leaders to keep the focus on policy issues like school grades.

"As long as we fixate on the who, the what goes unfixed," Carvalho said in a statement. "There should be no celebration of the commissioner's resignation. For our children's sake, let's get accountability right."

Times/Herald staff writers Steve Bousquet, Cara Fitzpatrick and Michael Vasquez contributed to this report. Kathleen McGrory can be reached at kmcgrory@miamiherald.com.