Amid calls for more practice-based teacher education, this article presents a concrete illustration of a practice-based bridging strategy for preparing high school biology teachers to enact open-inquiry labs. Open-inquiry labs were considered a core practice frame that served as a context for identifying core practices and for giving coherence to separate components of the approach to labs. A bridging model was developed in which the teaching practices, understandings, and intentions of 31 biology student teachers were elicited with respect to their current lab segments, and these were compared with the concrete segments of the core practice frame. From this analysis, a progression was developed to support prospective teachers in moving from existing conceptions of appropriate practice to a realization of the new practice frame as a better way to achieve valued goals.