A national leader in the Republican effort to overhaul public education resigned as Florida education commissioner Thursday, amid allegations that when he ran Indiana’s schools, he changed the state grade of a charter school founded by a prominent GOP donor.

In a resignation letter that surprised many, Tony Bennett dismissed the brewing scandal as “malicious and rooted in unfounded allegations” but said that it had created “a distraction from important work” and that he was leaving his post immediately.

The move came two days after the Associated Press reported that it had acquired e-mails written by Bennett in 2012, while he was running Indiana’s schools, in which he directed his staff to change the state grade for Christel House Academy. The charter school was founded by Christel DeHaan, who has given more than $2.8 million to Republicans since 1998, including $130,000 to Bennett.

The school, which had been kindergarten through eighth grade, added grades nine and 10 in 2012, and test scores from the new students were low enough to pull down the school’s rating from an A to a C on an A-to-F scale.

At Bennett’s direction, staff used a loophole in regulations and removed the scores of ninth- and 10th-graders, bringing the school’s grade back up to an A. Bennett has said that changing the grade made the rating system credible because he knew Christel House to be a high-performing school.

The Indiana State Teachers Association thinks otherwise. “It’s time to call the Tony Bennett letter-grading scandal exactly what it is — cheating,” union officials wrote in a statement. “There are no excuses for the actions taken by Bennett and his staff, as revealed in the string of e-mails, other than favoritism, cronyism, self-interest and hubris — none of which has a place in public school policymaking.”

As Indiana schools chief, Bennett forged a national reputation in Republican education circles. He oversaw Indiana’s use of tax dollars for private school tuition — the largest expansion of vouchers in the country — and he became a leader of Chiefs for Change, a group of state education officials created by former Florida Gov. Jeb Bush (R) that promotes charter schools, vouchers, and other policy changes. He is also a champion of the K-12 Common Core standards in math and reading, which aim to create national guideposts for learning.

“Tony started every day with the focus of creating a system that would equip kids to achieve their God-given potential,” Bush said in a statement Thursday.

Bennett lost his November bid for re-election in Indiana to Democrat Glenda Ritz, a former teacher who was critical of many of Bennett’s changes, including a requirement that students must be proficient readers by third grade or cannot progress to fourth grade.

After his loss, Bennett was quickly hired by Florida Gov. Rick Scott (R), who stood by him in recent days, telling reporters Bennett was “doing a great job.”

Bennett’s departure from Florida comes at a precarious moment in the state regarding the Common Core standards. Legislative leaders are calling for Florida to reverse its position and withdraw from the standards; Bennett was seen as its strongest advocate within the Scott administration.

Indiana had been rating schools since 1999, but it was under Bennett that the state switched to an A to F scale, which it used to determine the amount of state funding a school receives as well as whether it should be taken over by the state.

Michael Petrilli, a former official at the U.S. Department of Education and executive vice president of the right-leaning Thomas B. Fordham Institute, said that Bennett’s resignation could prompt discussion about the value of A to F school grading systems.

“I think there’s going to be a good conversation about whether boiling it all down to a single grade makes sense,” Petrilli said.