Mercer Island state Sen. Steve Litzow introduced a bill during the legislative session earlier this year that would give letter grades to schools throughout the state.

While the bill met criticism, a new report from the Washington Policy Center did just that — graded Washington schools.

The information was based on the state’s Achievement Index, a joint project between the state Board of Education and the Office of the Superintendent of Public Instruction, which has been in place since the 2008-2009 school year as a way to measure achievement in all schools in the state. It compares how schools do in reading, writing, math, science and graduation rates, and can be compared against other schools and districts.

The new report from the Washington Policy Center assigns letter grades to those index levels, ranging from exemplary to struggling. Schools earning an exemplary rating got an A, while those in the very good category earned a B, good earned a C, fair a D and struggling an F.

The grades were given based on information from the 2011-2012 school year, the most recent available from the state’s Achievement Index.

On Mercer Island, Island Park Elementary earned an A, while Islander Middle School and West Mercer Elementary both earned a B. Lakeridge Elementary and Mercer Island High School hit the good mark for a C.

Jennifer Wright, the executive director of Mercer Island’s learning and technology services said the reason for the difference is a slight change over the last time period when the school’s were measured.

Both Lakeridge Elementary and MIHS dropped very slightly in the improvement over previous year indicator, which was enough to drop the overall score to a lower category.

Wright said any time there is a so-called ‘negative indicator’ meaning a drop from the previous year, it will drop the overall score.

In the case of MIHS, the school’s overall score on the Index was 4.9, hitting the good category, while the cutoff for the very good category is 5.0. For Lakeridge, the school earned a 4.79, landing on the high end of the good category.

Other schools in the area received similar marks. Bellevue High School earned a C, while Interlake Senior High earned an A and Newport High School received a B. In the Issaquah School District, Pine Lake Middle School and Skyline High School both received a B grade.

Eleven other states in the U.S. use a similar system, assigning schools letter grades. The idea has been openly supported by Gov. Inslee.

In total, 11 percent of schools earned an A, 15 percent a B, 35 percent a C, 27 percent a D and 7 percent an F. The remaining 5 percent of schools were not rated for a variety of reasons.

To see a full copy of the Achievement Index database visit eds.ospi.k12.wa.us.