The purpose of this study was to investigate, through quantitative research, effective middle school characteristics that predict student achievement, as measured by the school-wide California API score. Characteristics were determined using an instrument developed by the Office of Superintendent of Public Instruction (OSPI), which asked middle school principals to rank predetermined characteristics of effective schools. Three hundred twenty five California middle schools comprised the population and sample of the present study. The analyses showed that nine researched characteristics (clear and shared vision, high standards and expectations, strong instructional leadership, high levels of collaboration and communication, curriculum, instruction and assessment aligned with standards, frequent monitoring of teaching and learning, focused professional development, supportive learning environment, and high levels of community and parent involvement) are positively and significantly correlated. The finding that the nine characteristics also had a moderate to high inter-correlation caused a problem for the researcher in determining the importance of a given predictor. Factor analysis reduced the number of independent variables and uncovered three factors that represent underlying relationships among the many variables. The three new factors. 11 were renamed the following: fostered school connectedness, focused standard based instruction, and clear and shared vision. Insights gained by this study may provide a direction for future or aspiring principals of middle schools and help them improve student achievement with the knowledge of the most significant factors impacting student academic achievement on the school-wide API score. In addition, these findings may have significance in helping schools form strategic plans of action that will meet the challenges of the No Child Left Behind Act. [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.]