This formative design study examines how a program curriculum and implementation was emergently (re)designed in dynamic relation to the expressed emotions of teachers and students. The context was a yearlong afterschool game design program for STEM learning at an urban and public all-girls middle school. Using Randall Collins' (Interaction ritual chains, Princeton University Press, Princeton, 2004) sociology of emotions framework, our analysis of field notes and video data reveal how the original intended curriculum hindered the generation of positive emotions, mutual foci of attention, and feelings of group solidarity--factors important in the generation of successful group interactions. In response to teacher and student expressed emotions, we took these factors as a guide for redesigning the program curriculum and implementation in order to foster a more positive emotional climate and redirect students' positive emotions toward engagement in learning goals. This study's implications point to the possibilities for designing curricula and program implementations to engender more emotionally responsive environments for STEM learning.