Recent literature casts unfavorable light upon the middle school as the most appropriate grade configuration in which to effectively educate young adolescents. The current criticism of middle schools may be fueled, in part, by "A Nation at Risk," the "No Child Left Behind Act," and a growing subsequent emphasis on accountability in U.S. education systems. Middle schools, in particular, have been implicated in a middle- grades achievement slump. As a result, many schools districts currently anticipate converting their middle schools into K-8 schools in hopes of improving student achievement. The reality of the situation, however, is that educational leaders too often face these decisions without an extensive body of specific empirical research on grade span-configuration and student achievement. The purpose of this dissertation was to gain a better understanding of the relationship between grade-span configuration and student performance, utilizing information collected by the state of New Jersey for use on school report cards. Specifically, the researcher analyzed proficiency assessment scores, attendance, and student discipline as measures of student performance during one school year. A statistical regression model was used to identify significant differences in student performance, including language arts literacy and math, and science achievement, between K-8 schools and middle schools. Socioeconomic variables, school size, and class size were included in most analyses to isolate the effect of grade-span configuration on the measures of student performance. The main result of the study was that students in K-8 schools outperformed those in middle schools on every student performance indicator except in the number of expulsions. The percentage of students who fell below the proficiency level in language arts, mathematics, and science portions of the state assessment was significantly higher in middle schools than in K-8 schools. Additionally, student attendance rates and comportment were significantly better in K-8 schools. The results of this study, consistent with those of other recent work, suggest that K-8 may provide a better opportunity structure for academic achievement. Grade-span configuration or something associated with it does appear to affect student performance, and therefore should be taken seriously as school administrators strive to improve student performance. [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.]