This study examined ways in which teachers use their own experiences and those of their colleagues to become better teachers, based on case studies of a group of eight physics teachers engaged in collaborative action research. Two perspectives on teaching that have framed other inquiries are first discussed: the teacher knowledge perspective, which specifies three forms of teacher knowledge (propositional, case, and strategic); and the teacher reasoning perspective, which focuses on practical arguments, practical theories, and the reflective practitioner. An alternative perspective is then offered, which makes distinctions between knowledge and understanding and between context and situation and which identifies three varieties of teacher wisdom--wisdom of practice, deliberative wisdom, and wisdom that relies on living and acting authentically in situations. Based on examination of the group's action research, a model for the generation and sharing of knowledge and understanding is developed, called enhanced normal practice, which involves three mechanisms: anecdote-telling, the trying out of ideas, and systematic inquiry. Implications of the study include: (1) for action research to have a long-lasting effect on practice, it needs to be self-sustaining; (2) research should be conceptualized as not only additions to categorizable knowledge but also as development of understanding; and (3) action research operationalized as enhanced normal practice could serve as a model of staff development. (Contains 54 references.) (JDD)