Purpose, scope, and method of study. The purpose of this study was to compare the effectiveness of eighth-grade single-gender classes with coed classes across subject area, gender, at-risk status, and socioeconomic status (SES). The sample was drawn from one school, DeSoto West Junior High School, where enrollment averages 80% African American, 10% Hispanic, 9% Caucasian, and 1% Native American or Asian. Sample sizes in each subject area were as follows: English N=894, history N=1,121, math N=885, science N=917. The dependent variable was academic achievement as measured by the final grade percentage. The study employed a quantitative causal-comparative design utilizing final grade percentages and demographic data from school reports. Analyses included an independent-samples t-test to compare single-gender classes to coed classes, a two-way ANOVA to compare each gender between class types, and a factorial ANOVA to ascertain interaction effects of low SES and at-risk students. Findings and Conclusions. Two research questions formed the basis of analysis. Results to the first question indicated that the mean scores of the single-gender classes in all subject areas were significantly higher than the mean scores of their counterpart coed classes. Further analysis revealed that the boys in the single-gender English, math, and science classes scored significantly higher than the coed boys. While the mean score of the girls in the single-gender classes was higher than the mean of their coed counterparts they were not significant statistically. In history, although the mean scores of the single-gender classes were significantly higher overall, neither gender scored significantly higher than their coed counterparts. Results to the second research question indicated that there were significant differences for SES, at-risk, and class type in each subject area. Each of these subgroups scored significantly higher in single-gender classes. However, no other combination of independent variables significantly affected the final grade percentages in each subject area, which indicated that single-gender classes did not uniquely benefit low SES or at-risk students. [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.]