This paper describes the struggles of one professional development project as it attempted to use networking technology to promote ongoing reflection and community building among its participating teachers. It employs Riel and Levin's (1990) framework for participant structures in computer networking environments to consider the strengths and weaknesses of the online portion of the project in terms of encouraging participation. The paper reports data from two consecutive cohorts of teachers showing how difficult it can be to establish online community participation as a component of teachers' work-life. The 17 participants in the first year of the Teaching Mathematics with Technology Project (TMTP) (2000-2001) were practicing secondary mathematics teachers (grades 6-12) from 9 different schools. Participants varied widely in terms of number of years of teaching experience (ranging from 1 to 25 years), mathematics courses taught (ranging from pre-algebra to pre-calculus to AP statistics), and experience teaching with educational technologies (ranging from almost no use to everyday use). All 11 participants in Cohort 2 (2001-2002) are practicing secondary mathematics teachers (grades 8-12) from 4 different schools. These teachers are very similar to those in the first cohort in terms of years of teaching experience (2-20 years), courses taught, and experience with educational technologies. Although the TMTP is an ongoing professional development program, this study reports data from the first two years of this project, referring to the two groups of participating teachers as Cohort 1 and Cohort 2. The goals of the TMTP are twofold. First, the project aims to familiarize secondary mathematics teachers with various educational technologies and to encourage them to consider how such technologies might be used to enhance their students' understandings of mathematics. A second goal of the project is to build a community of mathematics teachers who share an interest in teaching with technology and who can support their own professional development apart from their involvement in the TMTP. A threefold professional development strategy is employed: a summer institute, monthly follow-up meetings, and an online forum for professional networking. Two appendixes include follow-up activity sheets. (Contains 10 references.) (AEF)