This five-year research project is designed to enhance understanding of how online professional development environments contribute to teach learning, changes in classroom practice and changes in student learning in comparison to face-to-face professional development. Using secondary school teachers learning to use a reformed-oriented environmental science curriculum (Looking at the Environment - LATE), groups of teachers will be randomly assigned to one of three conditions. These are: (1)a traditional face-to-face workshop, (2)self-guided online professional development, or (3)online professional development guided by a facilitator and structured as a "short course." The content of the professional development is held constant over the three conditions and the online aspect is based on previous research and development activities (Knowledge Networks On the Web - KNOW). Various measures are used to assess impact including: (1) teacher backgrounds and beliefs surveys, (2)written tests of teacher concept knowledge, (3)post-professional development interviews, (4)classroom observations of teachers enacting the curriculum and (5)student learning measures based on the curriculum materials.