The Department of Education takes several factors into account to calculate A-to-F grades for Maine’s public schools.

One is a snapshot of how a school’s students ranked in a current testing cycle. There also is a “growth” or “progress” measurement, which quantifies test score improvement year over year. The growth component accounts for 25 percent of an elementary school’s score. Progress accounts for 40 percent of a high school’s score.

All schools must reach certain participation rates in state assessments. Any school with fewer than 90 percent of students taking the test gets an F. If a school has a participation rate of 90 to 95 percent, it gets a reduction of one letter grade. State officials said about 10 schools got failing grades based solely on their participation rates.

The grades now measure only reading and mathematics scores for proficiency. Education Commissioner Stephen Bowen said he is open to considering other criteria in future years. The education department said it wanted to measure only a few familiar measures for the first report cards, to keep the system simple and easy to understand. That’s why the department is not assigning “plus” or “minus” grades, officials said.

Among the possible future measurements: SAT scores, attendance rates, dropout rates, writing scores on standardized tests, federal annual yearly progress status, Advanced Placement participation, and parent, student or teacher surveys. Several people have mentioned science assessments, which are given in grades 4, 8 and 11.

The grades will be updated once a year, and will be used for all public schools, including charter schools and the state’s 11 town academies. They will not be used to rate private schools or career and technical schools. Some schools are exempt because they are new or do not have sufficient data.

The criteria for grading elementary schools (grades 3-8) and high schools (9-12) are slightly different.

For elementary schools, the state awards as many as 400 points, measuring six categories:

1. Proficiency, 50 percent of score (200 points): This measures the percentage of students who scored proficient or above on the New England Comprehensive Assessment Program in mathematics and reading. The school gets as many as 100 points in each subject, so a school with a 70 percent score in mathematics and a 60 percent score in reading would get 130 points out of a possible 200.

2. Growth overall, 25 percent of score (100 points): This measures the collective growth of individual students from the previous testing year. First, the state awards points to each student from 0 to 1.4, based on a grid scoring system. The system awards 1.4 to a student who improves from the lowest ranking (“substantially below proficient”) to the highest ranking (“proficient with distinction”). The state then takes the total growth points in a subject in a school, divided by the number of all students used in the calculation, for a maximum of 50 points for both mathematics and reading.

3. Growth of bottom 25 percent, 25 percent of score (100 points): With the same scoring system for growth overall, this measures growth only among students who scored in the bottom 25 percent in the previous testing year, for a maximum of 50 points for both mathematics and reading.

What’s the grade? A = 300 plus. B = 280-299. C = 225-279. D = 200-224. F = Less than 200

For high schools, there is a total of 500 points in six categories:

1. Proficiency, 40 percent of score (200 points): This measures the percentage of students who scored proficient or above on the Maine High School Assessment and the Personalized Alternate Assessment Portfolio in 11th grade in both mathematics and reading.

2. Progress, 40 percent of score (200 points): This measures the most recent three-year average of proficiency in both mathematics and reading, plus the difference between that average and the previous three-year average. For example, comparing the average of 2012, 2011, 2010 to the average of 2011, 2010, 2009. The school gets as many as 100 points in each subject.

3. Graduation rate, 20 percent of score (100 points): The state multiplies the school’s four-year graduation rate by a maximum 50 points, and multiplies the school’s five-year graduation rate by a maximum 50 points.

What’s the grade? A = 350 plus. B = 300-349. C = 225-299. D = 200-224. F = Less than 200.