Public school letter grades, which have sparked controversy since they were unveiled in 2011, are at the center of a new dispute between state education leaders and local superintendents.

Louisiana's system for assigning schools and districts yearly grades is undergoing major changes. Local educators say it will mean a startling plunge in A's and an uptick in F's.

"I think with the new accountability system you are going to have a major drop in scores," said Scott Devillier, superintendent of the top-rated Zachary School District and a member of the influential Superintendents' Advisory Council.

Under one scenario, the number of A-rated schools would drop 47 percent in 2018 and F-rated schools would shoot up by 80 percent.

"Everybody is concerned about how do we explain those types of things," Devillier said of falling scores.

But Gary Jones, president of the state Board of Elementary and Secondary Education, said the tougher benchmarks have been endorsed by both the current and previous BESE.

"The reality is we have to increase the standards," said Jones, a veteran educator who lives in Alexandria.

Letter grades have been a thorny topic for the past six years, when the initial round of ratings showed that 44 percent of public schools were rated D and F.

Schools and districts have improved since then, but the annual release of school and district marks is always an anxious time.

The issue dominated a meeting of the superintendents council on Friday, which followed weeks of private talks among state Superintendent of Education John White, local superintendents, BESE members and civil rights groups.

"This is one of the tougher calls in the system we have designed," White told the group.

More talks are planned, and BESE, which had three members at Friday's meeting, may take up the issue in October.

The state, under action that BESE took in March, is gradually raising the bar as part of its plan to improve schools under the federal Every Student Succeeds Act.

Cade Brumley, president of the superintendents group, said he hopes a compromise is forged between local superintendents and state officials to stave off major problems.

"Under the proposed formula, the number of traditional public schools, as well as public charter schools, with an A rating will drastically fall and the number of F-rated schools will substantially increase," he said in an email response to questions.

Brumley is superintendent of the DeSoto Parish school system in northwest Louisiana.

Under the current grading system, schools and districts are assigned letter grades based mostly on how students fare on key tests.

The state long relied on the third highest of five levels — basic — in determining whether a school got an A rating.

That bar is gradually being raised to the second level — mastery — for the top rating.

Critics contend the scoring scale under review needs to be revamped to better reflect student achievement and more credit for students who score in the most common category — basic.

Key superintendents favor a grading scale which, in 2018, would mean A-rated schools would drop just 14 percent and the number of F-rated schools would rise by 28 percent.

Scott Richard, executive director of the Louisiana School Boards Association, said the state's initial proposal would make it hard for schools and districts to earn a B.

"We are raising the bar, and yet there are still a lot of unknowns," Richard said.

He said an independent evaluator is needed to review the grading scale and ensure that assumptions being used by the state Department of Education on the impact of the changes are valid and reliable.

Others said the new benchmarks, which start taking effect for the current year, are a key part of Louisiana's move to issue grades using the rigor common in other states.

"The standard we have been using, when we first started labeling these schools as A's and B's, was a much easier standard than what the rest of the country was using to describe as successful," said Jim Garvey, a BESE member who lives in Metairie.

Garvey noted that state computer projections forecast a drop in the number of A-rated districts and an increase in those with F's.

"But not an end-of-the-world scenario," said Garvey, an attorney and a former BESE president.

School and district letter grades for the current school year will also mark an end to the state's use of a curved system for the past five years, another source of anxiety for some local superintendents.

That kept the distribution of A's, B's and C's the same from year to year during the move to tougher academic standards in English and math.

The new scoring system will also allow yearly academic growth to account for 25 percent of the score, not the 7 percent used in the past, which was limited to struggling students.

"I think, instead of how many A schools we have and how many B schools we have, we should be focusing on which schools are producing the best improvements in our students," Garvey said.

Follow Will Sentell on Twitter, @WillSentell.