A web site for an online graduate course in Earth systems science for middle school teachers was designed to affect teachers' knowledge about Earth systems science and resources and their use of constructivist teaching practices, particularly collaboration, rubrics and the use of journals. In the 16-week course 44 teachers experienced collaborative inquiry as they worked in groups to develop knowledge of individual spheres and create Earth systems diagrams as teams. Individually, they created Earth systems science lessons and local event analyses. Teachers were administered an exploratory pre-course survey to guide ongoing development and formative assessment. A post-course survey provided information on the validity of the design and its affect on the participant's attitude changes; knowledge gains, time spent and suggestions for further improvement. An archive analysis is currently underway. Revisions to the site design and content, the course methodology and assessment tools are discussed. (Contains 26 references and 15 figures.) (Author)