Grew and Sheldrake found that Christel House's initial "C'' prompted changes across the grading formula, but said the changes were applied evenly among other schools.
Education leaders interviewed for the report said they believe the Indianapolis charter school is a top-performing institution, but also said Bennett's formula did not earn their "trust" because of a lack of transparency.
"Through our interviews, we learned that Dr. Bennett had been under considerable pressure to design an accountability system that was not deemed harsh to charter schools or urban schools," they wrote. "In response to such concerns, he repeatedly stated that Christel House Academy, which was widely viewed as a successful charter school in an urban environment, would do well under the new system."
The initial "C'' Christel House received was "a surprise to Dr. Bennett and senior DOE staff," Grew and Sheldrake's report said. Efforts to raise the school's grade were both an attempt to save the credibility of the New Accountability Model and a desire to treat a recognized good school fairly, according to a wide range of testimony.
"Any further motivations underlying these actions are beyond the scope and documentation of this report," Grew and Sheldrake said.
Bennett resigned as Florida's schools commissioner a few days after The Associated Press published emails showing he changed Indiana's school grading formula for Christel House. The school was founded by a prolific donor who has given roughly $2.8 million to Indiana Republicans in the last 15 years.
Bennett said in a statement Friday that the report is "vindication" against "political attacks" levied against him.
"The report clearly shows that accusations of manipulation of the A-F system for a single school are false and malicious," Bennett said. "I am pleased with this vindication, not for me, but for the work of my colleagues at the Department of Education and for the 1.1 million Indiana students who have benefited and will continue to benefit from a clear and rigorous school accountability system."
Grew and Sheldrake said Friday that the report does not "exonerate" or "vindicate" Bennett, nor condemn him. They said it only explains how his team changed the grading formula.
Senate President Pro Tem David Long, R-Fort Wayne, said he hopes the findings allow education leaders to move forward with a rewrite of the school grading formula, which was called for months before Bennett's emails were published.
House Speaker Brian Bosma, R-Indianapolis, said he did not think "benchmark" schools, like Christel House, would be used in the new system to set the formula.