The purpose of this causal comparative study was to examine effect of the K-8 grade span configuration on the academic achievement of 8th-grade students in the State of Georgia, and to determine the viability of the K-8 grade configuration as a strategy for improving the academic achievement of students at the middle grade levels. This study examined the aggregate Criterion Referenced Competency Test (CRCT) performance of 8th grade students in Georgia. Purposeful sampling included 25 K-8 and 25 middle schools of various locations, sizes, and organizational structures (charter and traditional public). Comparisons were made between the achievement levels of students in the two structures, K-8 configuration and the traditional 6-8 middle school. Academic data was examined as a whole and according to demographic subgroups, which include race, gender, disability, and socioeconomic status. Groups were compared using independent samples t-test and multiple linear regression. The results of this study indicate that there is not a significant difference between the academic achievement of eighth-grade students who attended a traditional middle school and the academic achievement of those students who attended a school with K-8 grade configuration with regard to their Georgia CRCT mathematics and reading passing rates regardless of race, gender, disability, and socioeconomic status. The lack of a difference persists even after statistically controlling for school size, school location, and organizational structure. K-8 grade span configuration has no effect on academic achievement as measured by Georgia CRCT mathematics and reading performance. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]