To promote large-scale science education reform, developers must create innovations that teachers can use to learn and enact new practices. As part of an urban systemic reform effort, science materials were designed to reflect desired reforms and to support teacher thinking by addressing necessary content, pedagogy, and pedagogical content knowledge for teachers. The goal of this research was to describe teachers' enactments in comparison to reform as instantiated in the materials. Four middle school teachers' initial enactment of an inquiry-based science unit on force and motion were analyzed. Findings indicate two teachers' enactments were consistent with intentions and two teachers' enactments were not. However, enactment ratings for the first two were less reflective of curriculum intent when challenges were greatest, such as when teachers attempted to present challenging science ideas, respond to students' ideas, structure investigations, guide small-group discussions, or make adaptations. Overall, findings suggest that purposefully using materials with detailed lesson descriptions and specific, consistent supports for teacher thinking can help teachers with enactment. However, materials alone are not sufficient; reform efforts must include professional development and efforts to create systemic change in context and policy to support teacher learning and classroom enactment. ß 2005 Wiley Periodicals, Inc. J Res Sci Teach 42: 2005 To promote goals established for student learning, reform efforts in science education have focused attention on classrooms and how teachers can improve their instructional practices. Reformers encourage teachers to use inquiry supported by use of technology tools to promote Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. More information about this work, including the curriculum materials ''Why do I need to wear a bike helmet?'' used in this study, can be obtained from our project's website