This design research study explored the potential of Curriculum Support Materials for promoting teaching as design. Conducted over a four-month period, the study traced the design, development, and pilot testing of a web site intended to serve as a professional development resource for teachers. The purpose of this exploratory study was to evaluate the web site's potential for promoting elementary mathematics teachers' understanding of teaching as a design activity and for supporting teachers in engaging in teaching as design. A team of four second grade teachers tested the web site during a two-week pilot unit on introducing the concepts of multiplication and division. Qualitative data were collected from these teachers through a planning and teaching log, a post-unit questionnaire, and a post-unit focus group interview. The findings indicated that the web site had the potential to promote teachers' understanding of teaching as design, but that the web site's potential as a stand-alone resource for supporting teachers in engaging in teaching as design was limited. Two specific features of the web site, the Unit Checklist and the videos addressing the related mathematics content, were identified as potentially valuable resources that could be incorporated into an ongoing professional development experience. Suggestions for revisions to the web site are discussed along with recommendations for further study.