This article outlines the results of an issues-based study conducted over a 12-month period that investigated how the systematic inclusion of teachers within the design, operationalization and implementation of an online curriculum development project in Florida led simultaneously to teachers' own professionalizing in areas of education they were previously unknowledgeable. Specifically, this study charts how reflective, iterative curriculum development practices acts as a mechanism for in-servicing, leading to more informed teacher practices in the classroom. The investigation revealed that while the project was ambitious in its scope, it achieved its primary objectives through the implementation of deliverables outlined for the first year of the project. Research outcomes indicated that within the "situated" process of socialization into a community of practice, teachers' cognitive growth can be prompted by an individual's receptiveness, sensitivity towards and ability to manage mediational means placed at his/her disposal. A more acute receptivity towards appropriating mediational means, a sensitivity towards identifying the quality of using such mediational means in terms of their own microgenetic growth and an ability to manage such means within interactional operations ultimately shaped the extent of learning in the teacher's own zone of proximal development. (Contains 2 figures and 2 notes.)