During the 2009-10 school year, 42% of the students failed the biology segment of the EOCT, which affected not only the final grades of these students, but also overall school accountability. These results instigated some questions about the factors associated with students' success in biology; some of those factors related to the merit of single- versus mixed-gender classes. The purpose of this quantitative comparative study was to determine whether students attending single-gender biology classes taught by teachers of their own gender earn higher overall semester averages, as well as higher scores on the biology segment of the Georgia End of Course Test (EOCT), than do students attending mixed-gender classes. A rural high school located within the southeast region of the state of Georgia served as the study site. Social learning theory and social cognitive theory provided the conceptual framework of the study. The scores and semester averages of 84 ninth-grade students were analyzed using both descriptive and inferential statistics, specifically the independent t test. In comparison to mixed-gender classroom structures, classrooms that were led by female instructors with female students generated higher means in both semester averages as well as the biology segment of the EOCT; however, these differences were not statistically significant. Despite the nonsignificant findings, single-gender classes continue to present merit, especially for reducing teacher "burnout" and involving a greater number of girls entering science influenced careers. As long as a gender gap exists within the fields of science and mathematics, more research is needed so all students have the opportunity to achieve their maximum potential within the sciences, both academically and throughout their careers, regardless of their gender. [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.]