In the research study, this investigator utilized a non-experimental, causal-comparative design (ex post facto) with archival data to determine the real impact single gender instruction had on eighth grade students' mathematics achievement. The purpose of this study was to quantitatively analyze the benefits of single gender mathematics instruction for eighth grade male and female students, when compared against traditional coeducational instruction. Specifically, the researcher compared students instructed in single gender eighth grade mathematics classes with students taught in traditional coeducational classes by analyzing fall vs. spring Measures of Academic Progress (MAP) computerized mathematics test score means. Additionally, honors vs. non-honors level groupings were analyzed. The number of students being studied (over 2,000 total from across South Carolina) and the instrumentation being utilized (Northwest Evaluation Association's (NWEA) MAP national assessment) distinguished this research project from previous studies and gave it additional validity and reliability. The mean difference in students' fall vs. spring MAP scores were analyzed utilizing a two way analysis of variance (ANOVA) to determine the impact of each main effect as well as an examination of the interaction of both effects. The research showed that the type of instruction (single gender vs. coeducational) and the interaction between the type and level of instruction did not have a significant impact on the students' overall achievement. The level of instruction (non-honors vs. honors) did have a significant effect on the students' learning with non-honors students outperforming honors students on the MAP assessment that was administered. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]