This report provides a comprehensive description of the purpose, theory, methods, measurement development, and results of the ExCELS descriptive study. The study had two objectives: (1) to develop a new measure of ECE leadership that meets standards for reliability and validity to support its use and (2) to examine empirical support for the associations among key constructs and outcomes in the theory of change of ECE leadership for quality improvement. Chapter I presents the goals of the ExCELS project as a whole and the research questions for the descriptive study. Chapter II describes the ExCELS theory of change and the conceptualization of the leadership measure. Chapter III discusses the methodology of the ExCELS descriptive study. Chapter IV details the process to develop the ExCELS measure and presents the psychometric properties of the leadership scores. Chapter V explains the construction of the leadership scores; examines variation in the scores by staff and center characteristics; and assesses the concurrent validity of the scores to an external, validated measure. Chapter VI presents variations in formal management and staffing structures across centers and examines the associations between these formal structures and leadership scores. Chapter VII presents results of the analyses to test the ExCELS theory of change by examining the associations between influences on leadership, the leadership scores, and the outcomes that leadership might influence. Chapter VIII provides a summary of key findings, potential uses of the leadership measure, and next steps for refining and further testing of the ExCELS measure. (author abstract)