The Classroom Assessment Project to Improve Teaching and Learning (CAPITAL) examined teacher change and development with regard to classroom assessment. The National Science Foundation supported the four-year effort to study how teachers modify their practices to create the conditions for the kinds of assessment that foster learning. The authors set out to investigate how more than 25 teachers grappled with both personal and professional challenges to try to become the kind of the teachers they wanted to be, and how this played out in terms of the assessment culture they sought to create in the classroom. The authors were guided by such questions as: What are teachers' assessment practices? How are they shaped? How do teachers actually improve their day-by-day assessment efforts to enhance students' learning? And how might a research team from Stanford University lend a hand? In this article, the authors explore the personal nature of change in teachers' classroom practices. Through case studies of two teachers who worked intensively with CAPITAL, the authors examine the connections between who the teacher is--his or her beliefs, priorities, and propensities--and the nature of changes that the authors saw in them and their classrooms with regard to assessment. The authors discuss the approach that CAPITAL researchers used in their work with teachers and propose some lessons learned for others who seek to support instructional change in classrooms. (Contains 1 note.)