The current study explored how a STEM coach supported an elementary teacher during the implementation of an integrated curriculum that culminated with an engineering design challenge. The findings of the case study reported, detail how the reflective nature of the coaching moves employed failed to fully meet the needs of the teacher given the distinct challenges that arose upon implementation of the co-developed curriculum. By closely examining two primary data sources: (1) five extended coaching sessions, and (2) the coach’s pre-post coaching log reflections; analysis identifies and explores how the pair’s missed expectations produced unanticipated tensions that hindered the potentials of the teacher-coach relationship. Insights related to an elementary teacher’s conceptions of STEM integration are also revealed within the data presented. Finally, analysis enabled discussion of strategies that might be employed to strategically support elementary teachers working with coaches; specifically exploring how differentiated supports based on prior experiences might be instituted.