The purpose of this study was to compare the academic performance of students enrolled in coeducational instruction and single-gender instruction. Within this framework, the researcher examined class type, gender, and racial/ethnicity using the sixth grade CRCT scores of selected students in the areas of mathematics and science. The fifth-grade mathematics and science scores for the same population were used to control for prior knowledge. This study examined the academic achievement of students based on class type, gender, and racial/ethnicity in relation to academic achievement. The study included the CRCT scores for mathematics and science of 6th-grade students at the middle school level who were tested during the 2007-2008 school year. Many studies conducted in the past have stressed females performed better in mathematics and science, while others have stated males performed better in the same areas. Yet, other studies have found conflicting results. A large Australian study (1996), compared the academic performance of students at single-gender and coeducational schools. The conclusion of this study indicated that both males and females who were educated in single-gender classrooms scored significantly higher than did males and females in coeducational classes. A study conducted by Graham Able (2003) documented superior academic performance of students in single-gender schools, after controlling for socioeconomic class and other variables. Able's most significant finding was that the advantage of single-gender schooling was greater for males in terms of academic results than for females. This directly contradicted the educational myth that males performed better in classrooms if females were present. The sample in this study consisted of CRCT scores for 304 sixth-grade students from four different middle schools. Due to the racial composition of the sample, the study only focused on black and white students. School 1 and School 2 involved single-gender instruction while Schools 3 and School 4 involved coeducational instruction. A sample of eighty students was taken from each of the middle schools with single-gender instruction and a sample of 72 students was taken from each of the middle schools with coeducational instruction. Prior to conducting the study, an extensive application was filed with the local board of education to request permission to conduct research in the county. This process involved a detail description of the sample, sampling procedures, sample size, staff members, grade levels, and background information for the study. The major findings in this study indicated that the coeducational students outperformed the single-gender students and the white students outperformed the black students. This study confirmed that white coeducational students performed significantly higher than the black coeducational students. It was also documented through this study that there was no significant difference between the performance of the single-gender black students and the single-gender white students. In contrast to the Australian study (1996), this study indicated that the coeducational students were outperforming the single-gender students. In comparison to the 2003 study by Able, the findings of this study showed single-gender instruction was greater for females in terms of higher academic achievement than for males. [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.]