This research highlights a university-school division collaboration to pilot a professional development framework for integrating STEM in K-8 mathematics classrooms. The university researchers worked with mathematics coaches to construct a realistic and reasonable vision of STEM integration built upon the design principles of model-eliciting activities (MEAs). Analysis of participant reflections after they experienced two MEAs as learners in mixed grade-level teams suggests an evolving conceptualization of STEM integration with an explicit connectedness to mathematics content. Mathematics coaches valued the potential for MEAs to provide multiple entry points to open-ended problem solving, but they articulated a sense of vulnerability as they contemplated the challenges of time and teacher buy-in within the contextual realities of curriculum pacing and standardized test preparation. [For complete proceedings, see ED581294.]