Public schools around Indiana will learn their final grades next week under a ranking system using new rules that critics say are too complex for schools and parents to understand.

The State Board of Education is scheduled to approve grades for the more than 2,000 public schools across the state on Wednesday. The system, based largely on student standardized test scores, gives schools and districts A-F grades instead of ranking them by categories such as "academic progress" and "probation" as had been done until 2011.

But this year, the grades are based on new rules that critics claim are inaccurate and unfair. The state board approved the new rules in February over widespread opposition ranging from teachers to the Indiana Chamber of Commerce.

Much of the criticism revolves around the way the new evaluation system measures student growth. Students only get credit for "high growth" if their gain is better than two-thirds of all students at their testing level. That means only a third of students will be able to reach it, no matter how much their scores go up.

Supporters, including state schools Superintendent Tony Bennett, say the new way gives schools more credit when students' test scores grow faster than their peers, and provides more information and greater flexibility than the old system.

"It used to be strictly on a pass-fail system, and that's no longer the case," Bennett, who is running for his second term, told The Associated Press in an interview this week.

Bennett's opponent, Glenda Ritz, has made an issue out of the new evaluation system, saying the rules are so complicated even Bennett's own department doesn't understand them.

Last year, the grades were released in August. They were supposed to be released Oct. 10 this year, but that was delayed until Oct. 31 after the Department of Education was bombarded with questions and several school districts filed appeals, The Journal Gazette of Fort Wayne reported.

Bennett said the agency wanted to give schools and districts more time to examine the preliminary results they received in September.

"My No. 1 goal was to get it right and to provide a clear picture of how schools perform," he told AP.

Ritz, however, said she suspects the grades' release to be delayed again—until after Nov. 6.

"I don't think Tony is going to release the results until after the election, because most schools are going to receive D's and F's," she said.

The grades will reflect schools' performances during the 2011-12 school year.

East Allen County Schools Superintendent Karyle Green told The Journal Gazette that the calculations used in the new system are so difficult to fathom they cause people to lose confidence in the results. She also questioned the way student growth is measured.

"The ideas behind what they're trying to do have positive merit, but because it's so new, nothing appears to be going as planned," she said.

Green also questioned how schools could usefully apply the grades when they aren't released until months into the school year.