If practicing teachers are expected to be reflective practitioners, as teacher standards require, they must understand what reflection means. The problem addressed in this research study concerns the confusion about the meaning of the term reflection in education. The purpose of the study was to develop substantive theory about the relationship between teachers' reflective thinking and the development of their reflective practices. Foundational literature of the reflective thinking theory of Dewey, Schon, Zeichner and Liston, Brookfield, Mezirow, and Kegan was used in this study. Through an inductive constructivist methodology based in Glaserian grounded theory, the question of how practicing teachers describe reflection, use elements of reflective thinking, and apply these elements in their practice situations was investigated. Responses were developed to 5 subordinate questions that inquired through personal interviews with 15 teacher participants about (a) their descriptions or definitions, (b) their activities, (c) their uses, (d) their purposes, and (e) their application strategies of reflective thinking. Through constant comparison analysis of data, a definition of reflective thinking, including the elements of reflection, and three descriptors to the definition emerged from consideration of the data. A substantive theory resulted that those participants who accessed their capacity to engage the full complexity of the reflective thinking process showed considerable growth toward the development of reflective teaching practice. Implications for social change include a foundational vision and mission for learner-centered graduate education and professional development in which teachers learn to use reflective thinking to guide and direct their own professional development so that they may serve their own learning needs in order to serve the varied needs of their students. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.