This book represents the results of a 15-year study based on case studies of the development of four teachers' pedagogical thinking. It illustrates how teachers' thinking (about children's behavior, development, learning, and teaching) develops over time based on their personal and professional life experiences. Data come from regular, periodic interviews with and observations of four teachers who graduated from the University of California Berkeley's Developmental Teacher Education (DTE) Program. Part 1 situates the study in theory and research on teacher development, describing the theoretical perspective of the DTE program that grounded the research and explaining the qualitative research methodology. Part 2 offers the case studies, which illuminate how each person's pedagogical thoughts and actions developed over time and show how each teacher's thinking played out in the classroom. Extensive quotes embedded in the case studies allow the teachers to tell much of their stories in their own words. Each case ends with teachers' own words based on recent reflective writing. Part 3 reviews the cases to examine such issues as whether teachers lose what they learned during teacher education, how teachers' pedagogical understanding grows and changes over time, and what other theories of teacher development have to say about teachers' lives. (SM)