Sweeping changes to Indiana's A-to-F ranking standards for public schools have been approved despite complaints that the new rules are too complex for schools and parents to understand.

The State Board of Education voted 6-2 Wednesday for the changes. The overhaul means the grading scale for Indiana's schools will now be attached to a new evaluation system that gives schools more credit when students' test scores grow faster than their peers, The Indianapolis Star reported.

The changes also add new measures to gauge how well schools prepare students for college and careers.

A wide spectrum of educators and education-focused groups opposed the rules, however, calling them too complex. They also said one growth measure was potentially unfair to schools.

Board members said that while the system is not perfect, it provides more information and greater flexibility than the old system.

State schools superintendent Tony Bennett said complexity could not be avoided in getting a deeper understanding of school performance. Bennett also said the new policy is flexible and will allow education officials to "go back and revisit them" to make later changes.

Indiana replaced its school rating categories with A to F grades last summer, though the methods used to rank schools remained unchanged for 2011. Bennett had promised an overhauled school rating system for this year, and the changes approved Thursday spell out the criteria or logic used to determine each of those grades, said State Department of Education spokeswoman Stephanie Sample.

Indiana's public schools will get their first letter grades based on that new criteria this fall. The grades will reflect schools' performance during the 2011-12 school year, Sample said.

Indiana also sought a waiver from the accountability requirements of the federal No Child Left Behind law in its pursuit of creating a new system for judging school quality. The state submitted its new A-to-F proposal to show how it planned to do so.

Indiana is also implementing "common core" standards that will be shared by 45 other states and eventually bring new tests that could replace ISTEP, the state's standardized achievement test.

The new system is built on three primary test factors that judge if students have reached proficiency, how much they improved and how their growth compared to other students on their testing level.

But the growth measure has proved controversial.

Based on ideas borrowed from Colorado, it only gives students credit for "high growth" if their gain is better than two-thirds of all students at their testing level. Because this measure is percentage based, only a third of students will be able to reach it — no matter how much their scores go up.

Some educators worry that could handicap some schools if their students make solid growth but growth across the state is even better.

State Board of Education member Mike Pettibone raised that concern, saying the state should want a student's test scores to reflect at least a year's gain over a year's time.

But the model would allow students to be labeled "high growth" with less than a year's gain in test scores if students across the state did poorly in general. Or they could miss out on being labeled "high growth" even if they made more than a year's gain if students statewide scored higher than usual.

Board member David Shane argued that the system's advantages outweigh those weaknesses.

"I'm not sure I love all of it but I find it intriguing that schools are being judged on how well they got their kids to learn," he said.

Board member Jo Blacketor said she was most concerned by reports that schools and parents had difficulty understanding how their schools received their grades. A simulation of the new system saw some grades jump or fall dramatically.

Blacketor said A-to-F was supposed to be easier for parents to understand, not harder.

"It is not transparent to the general public," she said. "It is not simple. It is complex."