COBB COUNTY - Results of the Iowa Tests of Basic Skills show that Cobb County School District's third, fifth and seventh graders are performing better than the national average. In Marietta City Schools, fourth graders were on par with the national average in reading and above the national average in math, while the system's seventh graders were below the national average in both those categories.

In September, Cobb students in grades 3, 5 and 7 took the ITBS in reading, language, math, social studies and science. In Marietta City Schools, fourth and seventh graders took the tests in only reading and math. ITBS is a nationally norm-referenced test, and Georgia law makes norm-referenced testing optional, Marietta officials said. Cobb and Marietta schools use the results of the fall testing to assist and prepare students before they take Georgia's Criterion Reference Competency Tests in the spring.

The ITBS results "are a good indication that our instructional program is competitive on a national level," Cobb Superintendent Fred Sanderson said in a statement. "This assessment provides good data for our teachers to use early in the school year that will help them to identify areas of strengths and weaknesses, and prepare students for the critical CRCT."

The ITBS ranks student performance according to percentiles. For example, a student in the 75th percentile scored equal to or better than 75 percent of all students across the nation who took the test.

Percentile scores of 77 and higher are in the above average range, and scores of 1 to 22 are below average. That leaves a wide middle range, from the 23rd percentile to the 76th percentile, of average, though the 50th percentile precisely is noted as the national average.

Cobb's third-graders scored a composite ITBS score of 68th percentile.

Cobb's fifth-graders scored a composite of 66th percentile.

And Cobb's seventh graders scored a composite of 62nd percentile.

This year, the ITBS authors at the University of Iowa referenced the test to the performance of students who took the test in 2005, making comparisons with scores from prior years invalid, district leaders said. Tests in prior years are benchmarked to a control group of test takers in 2000.

This is the first year that seventh graders in Cobb have taken the ITBS. The district made the change from eighth-grade testing to seventh this year in part to see where students stand and allow more time for study, if needed, before the pass-to-advance CRCT tests in eighth grade.

Elementary schools with some of the highest composite percentiles in Cobb this year were Sope Creek (third grade composite 91st percentile, fifth grade composite 88th percentile), Timber Ridge (91st percentile, 85th percentile) and Tritt (90th percentile, 86th percentile).

On the other end of the spectrum in those grades were Belmont Hills (third grade composite 32nd percentile, fifth grade composite 40th percentile); Fair Oaks (32nd percentile, 31st percentile); and Green Acres (33rd percentile, 35th percentile).

For seventh graders, the highest achieving middle schools include Dickerson (86th percentile); Dodgen (85th percentile); and Hightower Trail (83rd percentile). Schools with lesser performances include Lindley (37th percentile); Smitha (39th percentile); and Garrett (41st percentile).

In Marietta City Schools, fourth graders scored a composite ITBS score in reading of 50th percentile, and a composite ITBS score in math of 53rd percentile.

Marietta's seventh graders scored in the 43rd percentile in reading and in the 49th percentile in math.

"We elected to test students in grades four and seven in preparation for the state-mandated CRCT in the gateway years, grades five and eight," Marietta Superintendent Dr. Emily Lembeck said in a statement. "... While seventh graders performed below the national average on two of the subject areas tested, ITBS results continue to be particularly helpful in identifying the skill areas where students may need additional instruction."

Schools in the Marietta system that had the highest percentiles in reading this year for fourth graders were Marietta Center for Advanced Academics (88th percentile) and West Side Elementary (72nd percentile)). Those two schools also had the highest percentiles for fourth graders in math (90th percentile for MCAA and 69th percentile for West Side).

The lowest percentiles in reading for fourth graders came from Dunleith and Sawyer Road elementary schools (both 33rd percentile). The lowest percentiles in math for fourth graders came from Dunleith (32nd percentile) and Lockheed Elementary (38th percentile).