School improvement initiatives rely upon effective leadership and organization at the state, district, and building level. Response to intervention models and similar multitiered systems of support are nationally implemented as frameworks for school improvement. This mixed-methods research focused on elementary principal leadership styles and building system implementation practices in four school districts. Explanatory sequential design emphasized multiple stages of data analysis and allowed data to sequentially guide each phase of research. The first phase, quantitative research, focused on internal and external variables impacting the underlying research questions. Two validated survey instruments were administered to evaluate the perceived leadership styles and perceived response to intervention implementation practices in each site. State-reported student achievement data and quantitative survey results were examined using Mann--Whitney U to determine if significant differences in leadership style and system implementation exist between low-achieving schools and their average- or high-achieving counterparts. Quantitative data collection and analysis then guided the second phase, qualitative research, to further explain the quantitative results. Qualitative focus group results were examined using theory-generated a priori coding. Results indicate significant differences in leadership style and system implementation practices exist between low-achieving schools and average- or high-achieving schools. [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.]