From the 한국일보.
High school students in Jeollanam-do's Jangseong county received the highest average scores in the country on the 2010 CSAT. The JoongAng Daily writes:
The Korea Institute for Curriculum and Evaluation released the test results yesterday of the 450,944 high school students nationwide who took the CSAT in 2010. Among all cities and counties nationwide, students in Jangseong County scored the highest in all four subjects - 116.5 in Korean language, 113.9 in Math-Ga, 125.1 in Math-Na and 119.6 in English language. Math-Ga and Math-Na focus on different tracks of mathematics and are geared towards the sciences and the liberal arts respectively.
You'll find the top ten regions in the four subjects listed above. As the article says, the county is home to an "autonymous private high school" 장성고등학교.
Ban Sang-jin, the school principal, said since the school changed to an autonomous school in 2008, it has attracted smart students from other cities, with about half of the students coming from outside the county. It is one of four high schools in the county. The county saw a significant improvement in CSAT scores since the autonomous school opened, the analysis found.Test results for individual schools and regions were first made public in 2009, to much fanfare. At the first release in April 2009, Jangseong county placed first in language, English, and Math-na, and third in Math-ga, according to figures from the 2008 exam. A 한국경제 article on this year's results says last year Jangseong placed third in language, second in math, and eighth in English.
According to more numbers via this chart from 쿠키뉴스, three of Gwangju's 구s placed in the top twenty in English, while Damyang county---home to another private school---placed 17th.
A November 2010 post provided links to the Korean college entrance exam questions for those interested in browsing.