Single-sex education is an instructional innovation implemented to improve student academic achievement by teaching to the learning styles and interests of boys and/or girls. This ex post facto quantitative study examined the differences in academic achievement between single-sex education and coeducation classes on students' achievement in literacy and math as manifested in fifth grade students' scores on the 2008 Arkansas Benchmark achievement exam. Fifth grade students attending a predominantly low socioeconomic elementary school in Fort Smith, Arkansas received the intervention of single-sex education for one year. Data were collected from the students' fourth grade 2007 Arkansas Benchmark exam and compared to the students' post intervention 2008 Arkansas Benchmark exam data to determine whether single-sex classes significantly improved academic achievement as measured by students' scores in literacy and math. The results indicated that there were no significant differences in academic achievement of fifth grade students in literacy and math. In addition, research available on the effectiveness of single-sex classroom instruction is reviewed. [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.]