AUGUSTA — Ninety-three of the 536 Maine schools that received a Department of Education-issued report card this week improved at least one letter grade over last year, according to a statement released by the department on May 15.

Data shared by the department showed that 155 schools dropped at least one letter grade, meaning more than half stayed the same. There are more than 600 schools in Maine, but some do not receive grades because they are too new or too small, according to the Education Department.

The report cards assign a letter grade to Maine’s schools based on how well students performed and improved on standardized tests and, in the case of high schools, the graduation rate.

Elementary and middle schools as a whole saw grades decline more than high schools. About 27 percent of Maine’s 414 elementary and middle schools that were graded received a D or an F, compared with 20 percent last year. The portion of high schools that received a D or an F stayed the same as last year, at about 28 percent.

The grading system was unveiled last year by Gov. Paul LePage’s administration with the intent of making data about schools more transparent and accessible.

The system has been controversial. The LePage administration believes that by using the A-F scale, “the report cards bring transparency to existing performance data,” according to an Education Department statement.

But to critics, the report card is too simplistic because it puts significant emphasis on students’ performance on statewide standardized tests.

“Schools, like students, are more than test scores,” said a statement from the Maine Education Association released Thursday. “The governor’s grading system, even with the additional information reported, still doesn’t ask for any input from those that are the most involved in student learning, the teachers, parents, principals and superintendents.”

Educators say the system is a better measure of school poverty levels than the effectiveness of a school.

“The formula disproportionately penalized communities with high levels of free and reduced lunch students,” said Bangor School Department Superintendent Betsy Webb on Wednesday.

A study by the Maine Education Policy Research Institute at the University of Southern Maine that was released in January backed that assertion.

“The level of poverty in a school is the single best predictor of average student performance,” the study states.

As a result, the report cards this year include the percentage of students who qualify for free and reduced lunch at each school. However, that information was not factored into the letter grades.

Also new this year is information on school funding, average daily attendance rates and school and district contact information.

David Silvernail, director of the Maine Education Policy Research Institute and author of the report, said the changes add needed texture to the report cards and are a step in the right direction.

“Schools and schooling is a complex endeavor,” he said. “Just putting one finger on the pulse of the school and saying, ‘here’s your academic grade,’ provides a simplistic picture.”

He said that despite the outcry, in some ways the report cards have achieved what they set out to achieve.

“It appeared that people, after they got over the initial shock, they started asking questions,” he said. “Why is my school not doing so well?”

That’s a question that students, teachers and administrators asked at the Deer Isle-Stonington Elementary School after receiving an F last year, according to the school’s principal, Mike Benjamin.

“When we got the grade last spring, everybody was devastated, including students,” he said.

In response, teachers began devoting more class time to test-taking strategies. Students worked through sample test questions and teachers taught skills such as process of elimination and the importance of rereading texts.

Benjamin said the school also provided an abundance of snacks to students before the exams.

Those efforts paid off. This year, Deer-Isle Stonington Elementary School got a C.

In elementary and middle schools, student scores on the New England Common Assessment Program account for 50 percent of a school’s grade. The other 50 percent is determined through a formula that calculates how much students improved on the exams. Each school receives a score out of up to 400, but schools lose points if less than 95 percent of their students sit for the exam.

Critics say the NECAP does not present a fair picture of school performance because it is taken in October.

“Children have three to four weeks of school before they are tested,” which is not enough time to show progress, said Webb.

High school grades are based on student scores on the the Maine High School Assessment, an adaptation of the SAT that only 11th-graders are required to take. High schools receive a score out of 500, 40 percent of which is calculated by performance, 40 percent by growth and 20 percent by graduation rate.

Next year, the system likely will change because schools will drop the NECAP and SAT for an exam developed by Smarter Balanced, a consortium of 21 states that have adopted new learning standards known as the Common Core.

In a statement released before the report card data became public, Jim Rier, the Maine Department of Education’s commissioner, urged schools to use the information to improve.

“The report cards that will come out today provide another learning opportunity for us all,” he said. “Some will be quick to dismiss the grades and the Department that delivers them, and I understand that. Others will use them exactly as we intended, seeing them as a snapshot of a school’s performance and a springboard for diving into the data to learn more about a school’s strengths and where there are opportunities for improvement.”

An earlier statement from the department said that 110 schools improved at least one letter grade, which later was revealed to be a calculation error, according to the Education Department’s director of communications, Samantha Warren. The correct number is 93.

To view report card data for all schools in Maine, visit http://dw.education.maine.gov/DirectoryManager/Web/Maine_report/MaineLanding.aspx.