High achievement in mathematics is a critical part of the portfolios of students seeking admission to the best high schools and colleges; it is essential to a school's success at district, state, and national levels and to America's future as a global competitor. Elementary school leaders need to provide their students with a balanced, comprehensive mathematics program that will lay the strong foundation students need to succeed in higher-level mathematics. Despite this need, many elementary principals lack the proficiency and confidence to supervise and improve mathematics instruction in their schools. The purpose of this study was to research, develop, test, and validate the "School Leaders' Guide to Elementary Mathematics" and give school leaders, district leaders, and instructional specialists who support elementary mathematics the tools and strategies they need to improve mathematics instruction and mathematics achievement in their schools. This qualitative study allowed the researcher to examine the background of instruction in mathematics, school leadership in mathematics, and the history of elementary mathematics instruction. It offered insights into the rich, detailed perspectives of the participants in this study and the relationship between school leadership and elementary mathematics. The "School Leaders' Guide to Elementary Mathematics," which is included in its entirety in Chapter V, features five sections: School Vision and Culture, Focusing on Instruction, Curriculum, Assessment and Data-Driven Instruction, and Professional Development. The researcher used an abbreviated form of Borg and Gall's (1989) research and development methodology, including an online anonymous survey to determine the efficacy of the "Guide." One hundred eight potential survey participants were identified using criterion-based purposeful sampling. All participants had roles in supporting elementary mathematics education, and all were interested in building the capacity of district, network, and school leadership in elementary mathematics. A qualitative approach using a combination of Likert-type and open-ended questions, a median and mode analysis of the Likert-type responses, and coding to categorize and analyze the open-ended responses allowed the researcher to identify common themes and ideas. The survey results support the need, development, and usefulness of the "Guide." Limitations and delimitations are also discussed. [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.]