This study focuses on the nature of professional development. The approach to professional development that emerged in this inquiry was premised on a belief held by the author, a university researcher, and two K-1 teachers that professional development opportunities for teachers need to be ongoing, allow time for teachers to engage in learning, and occur in a collaborative community of learners. Over an eight month period from October 2000 to May 2001, the researchers developed and implemented science curriculum that targeted a K-1 multi- age classroom of 40 students. One of the main objectives of the inquiry was to foster the development of teacher professional knowledge in the context of primary science education. The second objective was to explore the nature of the collaborative inquiry that emerged and its influence on the development of teachers' professional knowledge. Two questions guided this study: (1) How will the participating teachers enhance their professional knowledge as a result of this experience?; and (2) Under what conditions will this approach to professional development be effective? The processes and contextual variables that contributed to the overall effectiveness of the approach are identified and described as well as outcomes related to the development of collaborating teachers' knowledge base for teaching primary science. (SOE)