The Georgia Department of Education released graduation rates Tuesday using a new calculation method that significantly alters the 2011 scores of high schools across the state.
The new cohort graduation rate divides the number of students receiving a regular high school diploma at the end of the 2010-11 school year by the number of first-time ninth-graders in 2006-07, plus students who transfer in, and minus students who transfer out, emigrate, or die during the next four years.
The former method, called the leaver rate, calculated the number of diplomas awarded in a given year and divided by the total number of high school seniors, so the graduation rate included students who might have taken more than four years to finish.
“The new formula provides a more accurate, uniform look at how many students we are graduating from high school,” state Superintendent John Barge said in a news release.
The leaver method bloated numbers because it did not accurately reflect the number of students who dropped out before 12th grade or if a student took longer than four years to graduate, said Tara N. Tucci, a senior research and policy associate at the Washington-based advocacy group Alliance for Excellent Education.
The cohort method established Georgia’s average graduation rate at 67.4 percent last year. With the leaver rate, the state topped 80 percent in 2011.
Columbia County high schools showed a nearly 9 percentage point drop in graduation rate average using the cohort rate versus the leaver rate.
The school system’s average graduation rate for the 2010-11 school year using the leaver rate was 84.93 percent.
Using the cohort rate, the average graduation rate last school year in Columbia County is 75.95 percent.
The 8.98 percentage point drop, though, is slightly skewed.
State DOE figures exclude Grovetown High School from the leaver rate calculations last year because the new school had not yet had a graduating class that started there as freshmen. However, the cohort method does include Grovetown High’s 67.47 graduation rate in the new calculations.
Omitting Grovetown High, Columbia County’s average drop in graduation rate is 8.88 percentage points.
Greenbrier High fared best in Columbia County under the cohort rate with 89.01 percent, which is just 3.39 percentage points less than with a leaver calculation. Harlem High dropped 14.06 percentage points, from 73.3 percent to 59.24. Lakeside High fell more than 10 percentage points to 79.76 percent. Evans High’s graduation rate is 76.17 percent, a 7.73 percentage point drop.
Federal education rules mandate school systems use the new cohort rate.
In Richmond and Columbia counties, which have significant transient pupil populations because of a large military community, Columbia County schools Title 1 Director Lisa Soloff said the new Cohort Rate does provide a more accurate method to gauge schools dealing with numerous transfers each year.