MARIETTA - More than 80 percent of Cobb County's rising seniors have already passed all four graduation tests, the district said in a statement released late Thursday. At Marietta High School, 78 percent of students in the class of 2011 passed all four exams.

Still, though, the overall passing percentages are down from last year. Cobb's passing percentage in 2009 was 85 percent, and Marietta's was 90 percent.

"It is clear that our students are going to be competitive in their educational and career paths after they graduate next year," Cobb Superintendent Fred Sanderson said in the statement. District offices were closed Friday in a furlough day.

The two districts' average scores were the same - and higher than state and metro-Atlanta averages - in three of the four test subjects.

In English, Cobb and Marietta students had an average score of 246. The statewide average score was 238, and the metro Atlanta average was 241.

In math, Cobb and Marietta students overall average score was 540, compared with the state's 534 and metro Atlanta's 536.

In science, Cobb and Marietta students averaged a score of 242, compared with the state's 238 and metro Atlanta's 240.

In social studies, Cobb students averaged 242 and Marietta averaged 237. The statewide average is 233, and the metro-Atlanta average is 238.

"This is the first year the state has administered the new Social Studies tests based solely on the Georgia Performance Standards," said Marietta's superintendent, Dr. Emily Lembeck.

"While the data cannot be compared with prior year performance, I am confident that our teachers will work to demonstrate improvement in these test scores next year."

Students must pass all four tests and the writing test to graduate. Eleventh-graders first take the graduation test in the spring. They have at least four more chances to re-take any section of the test.

The English, science and social studies tests each require 200 points to pass. The math test requires 500 points to pass.

Cobb, in its release, also touted the "exceptional performance" at particular schools.

At Harrison High School, 100 percent of 11th-graders passed the math test, and Lassiter, Pope and Walton were close, with 99 percent passing in math.