The state's on-time graduation rate fell 1.6 percentage points to 72.1 percent for the Class of 2010.
"The bottom line for taxpayers is that slightly more than one in four students fails to graduate high school on time, and this is not acceptable," state Superintendent Mick Zais said in a conference call. "A one-size-fits-all approach doesn't work."
Aiken County's graduation rate rose 6.4 percentage points to 73.9 percent for the Class of 2010. Edgefield County's 2010 graduation rate was 72 percent, up 6.1 percentage points from 2009.
Both districts had "average" absolute ratings and "excellent," the highest, growth ratings. Only one school, Ridge Spring-Monetta High, had a "below average" absolute rating, and none got the lowest mark, "at-risk."
The absolute rating measures a school or district's academic performance in one school year. The growth rating measures the progress students make from one year to the next on state tests.
Aiken Performing Arts Academy, a charter school, was singled out as a high-poverty school that achieved "excellent" absolute and growth ratings. Zais said charter schools and other innovative programs, such as single-gender classrooms and Montessori schools, are an important part of offering programs suited to diverse learning abilities.
For high schools, the graduation rate is the biggest factor in determining the state ratings, but they also incorporate first-attempt pass rates on High School Assessment Program English and math tests, which students must pass to graduate with a diploma. Students typically take the HSAP exams for the first time in 10th grade and have several chances to pass it.
Kevin O'Gorman, Aiken County's associate superintendent for instruction and accountability, cited two factors in the district's improved graduation rate: more accurate tracking of students and an intervention program that began last year to identify rising ninth-graders at risk of not having a successful freshman year.
The state Department of Education this year tightened its requirements for proving high school students have moved out of state and didn't drop out. That was a big reason why the state delayed releasing the results of high school and school system report cards until today.
Other districts' graduation rates were hurt by the change, which apparently had the opposite effect in Aiken and Edgefield counties.
North Augusta High School's graduation rate shot up from 62.5 percent in 2009 to 76.9 percent in 2010. Its absolute rating improved from "average" to "good," and its growth rating went from "below average" to "average," in large part because of substantial improvement among historically underachieving student groups.
O'Gorman said he doesn't expect to see another big jump in the graduation rate, but he does anticipate a steady progression as the district's intervention program targeting at-risk rising ninth-graders gets more established.
Staff Writer Lynn Davidson contributed to this article.