This dissertation investigated the reasons that school districts chose to change the structure of their middle grades learning environments from the traditional junior high school to the newer middle school model. The study answers the following research questions: According to the perceptions of teachers, school and district administrators, and available documentation, in districts that made the change from junior high to middle school: 1. Why did the districts make the change from junior high schools to middle schools? 2. What obstacles to success needed to be identified before engaging in the transformation process? 3. How did district leaders effectively plan and subsequently execute plans to transform junior high schools into middle schools? 4. According to the Keys to Educating Young Adolescents of AMLE, which criteria for success have been met following transformation? This study focused on two school districts that engaged in the process over two decades ago yet currently maintain a school or schools recognized as Illinois Horizons Schools to Watch, exemplary examples of the middle school model. The study concluded that there are multiple factors, identified in the research as "themes" that contributed to successful transformation processes. These schools that changed their middle grades structures from junior high to middle school did so because they believed the middle school model better met the overall needs of students. Following the transformation processes the data from both districts demonstrated that the overall needs of students were better met in the middle school structure. [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.]