A new formula proposed to calculate school letter grades could result in fewer A-rated schools across Arizona.

With little more than a week to go before Arizona schools are to receive A-F letter grade ratings, the State Board of Education is still working out the formula used to calculate them, saying the options that have been drafted are significantly flawed.

The new formula, which was to be adopted on Friday, would have left Arizona with significantly fewer A-rated schools than the last time the grades were issued in 2014.

The A through F rankings have been on hiatus since Arizona switched from the AIMS assessment to the more difficult AzMERIT standardized test.

Under the formula, high schools that earned 70 percent of the points possible from all categories would be labeled “A” schools. For K-8 schools, the threshold would be even lower, with schools earning 60 percent of the points possible receiving the A ranking.

That bothered some board members, who noted that 60 percent doesn’t qualify as an A in the classroom.

But the board’s staff noted that if the cutoff were set at 70 percent, only 11 out of nearly 1,400 schools would qualify as A-rated.

“So clearly we saw that as problematic, and we readjusted,” Jen Fletcher, chief accountability officer at the Arizona Department of Education, told the board.

Complicating matters, the grouping for school scores is very tight, making it more difficult for the board to decide where to draw the line between an A and a B.

If the cutoff were set at 55 percent, for example, half of Arizona schools would be considered A-rated.

“If (the selected formula) were to be applied, we would have fewer ‘A’ schools, but the ‘C’s’ and ‘D’s’ are similar,” Fletcher said.

But State Superintendent of Public Instruction Diane Douglas said comparing the letter grades from 2014 to this year doesn’t make sense because the new grades would be based on different formulas with different testing systems.

“So it’s really kind of apples and oranges to a degree,” she said.

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The delay in adopting the standards called into question the board’s ability to stick to their timeline for issuing school grades.

“We’ve come so far on this road, it’s been a year and now we’re in the 13th hour and we’re looking at making changes, and some I understand and some I’m not sure about. But it ends up pushing the whole thing out. I mean, our schools are supposed to have their letter grades on (Aug.) 28th,” Douglas said.

The board had zeroed in on a formula that would consider proficiency on the statewide assessment, growth on the statewide assessment, proficiency and growth for English Language Learners and acceleration and readiness measures for K-8 students. For high school students the formula would also take into account graduation rates and college and career readiness.

The Arizona State Board of Education on Friday was unsure that the weights for each of the metrics, and how the formula used for each metric were calculated, was the right way to go.

So they delayed, and ordered staff members to further study several issues, tinker with the formulas and come back to the board with more information.

Douglas said she was disappointed the board couldn’t come to a decision, and worried that the delay would cost struggling schools time that they could use to improve.

“At some point you just have to make a decision,” Douglas said.

Contact reporter Hank Stephenson at hstephenson@tucson.com or 573-4279. On Twitter: @hankdeanlight