Her bill preserves the lessons learned from school grading, she said, while responding to the concerns of educators and looking ahead to the use of ACT testing as the state's year-end assessment for high school students.
"If we change from SAGE to ACT in [grades] 9, 10 and 11," Millner said, "we have to change the accountability system to align with that."
Since its creation in 2011, school grading has come under frequent fire from educators, who say the use of a letter grade based on test scores does little more than stigmatize schools based on socio-economic demographics.
And updates to the law last year created an automatically-adjusting grade scale that penalized schools despite widespread improvement on standardized tests.
Millner said the new system would avoid the complaints of moving targets by establishing criteria for each grade level.
Rather than a limited percentage of schools receiving an "A" or "B" and so forth, Millner said, any school meeting the established criteria would receive the appropriate letter grade independent of the performance of other schools.
The bill also awards points for participation in courses like Advanced Placement and for improvement among low-achieving students in an attempt to mitigate the correlation between school grades and poverty levels, Millner said.
"We've tried very hard to make this, what we call, as zip-code neutral as we can," Millner said. "We're taking into account that all of our schools have different demographics."
But the use of additional measurements is limited largely to high schools, Utah Education Association government relations director Sara Jones said. For elementary schools, she said, the formula for a school grade is altered but it is still tied to performance on year-end SAGE testing.
"We end up basing the letter grade again, still, solely on test scores," Jones said.
The bill also doesn't specify what the requirements for each letter grade would be. Instead, those decisions would be made by the Utah Board of Education with input from the governor, lawmakers, and school district representatives.
Senate President Wayne Niederhauser, R-Sandy, sponsored the original school grading bill in 2011. He acknowledged that the program has not worked as smoothly as intended, but spoke in favor of Millner's bill for preserving the state's focus on school outcomes.
"The structure, I think, is sound," Niederhauser said. "Now we need to decide how to fill in those blanks."
Terry Shoemaker, executive director of the Utah School Superintendents Association, said he had lost count of how many accountability systems the state has used over the last two decades, some of which were used simultaneously with contradictory results.