Of the 50 largest school systems in the nation, Montgomery County Public Schools continues to have the highest high school graduation rate, according to national data released Thursday.

In 2009, the latest year that data is available, 87.6 percent of Montgomery students graduated, according to Diploma Counts 2012, an annual study conducted by the Education Research Center and published by Bethesda-based Education Week magazine.

It is the fourth year that Montgomery has topped the list. The county’s graduation rate is far above the national and Maryland averages, which are 72.7 percent and 77.9 percent, respectively.

“These results would not be possible without the hard work of our students, the dedication and outstanding performance of our employees and the continued support and investment of our community,” Superintendent of Schools Joshua P. Starr stated in a press release.

Board of Education President Shirley Brandman said Thursday that everyone in Montgomery — teachers, staff, parents and students — must work together to ensure that students have opportunities beyond graduation.

“It is hard, dedicated work,” Brandman said. “There are no shortcuts. It is always important for us to stay focused so our students have more options when they leave us.”

Fairfax County Public Schools ranked second in the 50 largest systems, at 85.5 percent, followed by Jefferson County, Colo. and Baltimore County, Md.

The gap between Fairfax and Montgomery graduation rates widened between 2008 and 2009, according to the study — in 2008, 85.7 percent of Montgomery students graduated, while 85.1 percent of Fairfax students did.

The data released in the study differs from that reported by the Maryland State Department of Education.

The state department reported that, in 2009, 87 percent of Montgomery County students graduated, which is .6 percent lower than the Education Research Center reports.

In 2011, 90.7 percent of county students graduated, according to the state department.

For the past decade, Maryland used the “leaver rate” to calculate graduation rates; that rate did not reflect changes in the student population from freshman to junior year.

Under a new federal law, as of the 2011-2012 school year all states must calculate and report graduation rates based on a “cohort rate,” which takes into account which year each individual student first attended freshman year and changes in student population between freshman and senior year.

According to the four-year cohort rate, 86.8 percent of the county’s Class of 2011 graduated.

When the cohort rate is applied, Fairfax graduated a higher percentage of students in 2011 than did Montgomery.

In Fairfax, 92.5 percent of students graduated in 2011, according to data from the school system.

jbondeson@gazette.net