The Mathematics Learning Forums, a collaborative effort of Bank Street College and the Center for Children and Technology, Education Development Center, Inc., provided the primary research setting for this study. Each 8-week forum focuses on specific elements of a mathematics content area and is designed to address both student learning and teaching strategies. Participants are required to have an Internet account and are expected to participate at least twice weekly in online discussions. The forums provided the opportunity for an in-depth contextualized understanding of the experiences of 35 teachers involved in three 8-week online courses. The research design used a combination of data gathering tools including questionnaires (n=31), exit interviews (n=30), and content analysis of all public online exchanges (n=393). Six variables framed the professional interaction items: (1) teacher work group cooperation; (2) opportunities to exchange new ideas and instruction; (3) opportunities for reflection about practice; (4) capacity to give and receive feedback; (5) structures and norms that encourage a problem-solving approach to teaching; and (6) role of principal. Generally, the results showed that computer-based network professional development is far from reaching its potential. Many, but not all, of the remaining problems were technical issues. Teachers inflexibility and lack of familiarity with new technology were also obstacles to an online professional development program. (Contains 24 references.) (JLS)