AUGUSTA, Maine (AP) — Maine schools merited only a C grade while 31 percent of the state's high schools received a D or an F, under a new state grading system unveiled Wednesday by Gov. Paul LePage and Education Commissioner Stephen Bowen.

Maine becomes the 14th state to give letter grades to schools as LePage continues his offensive to shake up the state's public education system. The new system assigns A through F grades to more than 500 schools.

On the inaugural report card, 60 schools got A's; 75 B's; 289 C's; 76 D's; and 43 F's.

Flanked by students and legislators, LePage said the goal is to increase transparency and improve schools. Grading schools the way schools grade students should engage and motivate parents, communities and schools to identify shortcomings and improve, he said.

"We need to be sure our education system is first-rate," he said. "The only way we can assure that will happen is to look in the mirror and be critical of performance if we're not top-notch."

The grading system was blasted by superintendent, school board and teacher organizations, as well as Democrats, who called it flawed, biased against poor schools and nothing more than a public relations stunt.

"I think it's akin to kicking someone when they're down," said Connie Brown, executive director of the Maine School Boards Association. "Schools that receive poor grades generally have barriers they're trying to surmount, including poverty, and they're often in areas where they lack the resources to address their needs. To say they're now going to receive a letter grade is insulting and hurtful."

The Department of Education used existing data to develop a formula to come up with grades.

Elementary schools are graded on the results of math and reading assessment tests, and improvement in those scores year to year among all students and among the lowest 25 percent. High schools are graded using math and reading assessment tests, growth in those scores year to year, and graduation rates. School grades are posted on the Department of Education website.

Florida was the first state to grade schools by letter, in 1999, said Jaryn Emhof, spokeswoman for the Foundation for Excellence in Education, a Florida-based organization founded by former Gov. Jeb Bush. A flurry of states jumped on board after a 2009 federal report showed Florida had jumped from near the bottom of school testing to the near the top, she said.

Alabama, Arizona, Florida, Indiana, Louisiana, Mississippi, New Mexico, North Carolina, Ohio, Oklahoma, South Carolina, Utah, Virginia and New York City now give letter grades for their schools. The response among school administrators, teachers, parents and community members has been mixed.

Parents in Oklahoma have been supportive since the first school report cards were released last fall, said Oklahoma Department of Education spokeswoman Tricia Pemberton.

"School districts are still (complaining) about the formula, but parents are like 'thank you,'" she said. "People really wanted to see the grades their schools got."

But organizations representing Oklahoma school boards and school superintendents have been critical, going so far as to commission the University of Oklahoma and Oklahoma State University to evaluate the grading system. Their report, released in January, concluded that the system "falls short of providing a clear and credible picture" of individual school performance and doesn't provide reliable data on school performance.

Assigning grades is an overly simplistic way of evaluating schools, said Dan Domenech, executive director of the American Association of School Administrators, based in Alexandria, Va. The report cards typically don't consider discipline problems, parental involvement, teacher quality, student achievement and other factors, he said.

"There are a lot of factors that are swept under the rug when you just assign a grade," he said.

In Maine, Democratic Party Chairman Ben Grant said LePage is arbitrarily branding students and schools.

"From day one, Paul LePage has been on an ideological crusade to dismantle and destroy public education in Maine. Now he's hit a new low with his so-called grading system," Grant said.

But supporters say the way schools have been rated isn't understandable to parents and the public. They say letter grades will replace vague terms such as proficient, fair, struggling or needs improvement.

"Outside of education, most folks don't know what we're talking about," Bowen said.

Grading schools by letter is just one measure used to improve education along with school choice, early literacy skills, performance-based pay and online schools, Emhof said. She said some people have resisted the letter-grading system because it's new and demands accountability. But schools need to understand the system aims to improve education, she said.

"This isn't about just giving you a label and saying, 'Done, you're labeled, now we move on,'" she said. "This is about finding out what's going on. Nobody likes an F, but it stimulates action and we'll be here to figure out how to take you from an F to a D to a C to a B to an A."