Background: Science, technology, engineering, and mathematics (STEM) education is becoming more prevalent at the elementary level, and there has been a push to focus on the integration between the STEM disciplines. Researchers within this study sought to understand the extent to which triads composed of a classroom teacher, student teacher, and an engineering fellow were able to use the context of an engineering design challenge to integrate and incorporate STEM concepts into the elementary classroom. Using a content analysis approach, researchers analyzed STEM integration across four phases of learning: professional development workshop, lesson plan, classroom enactment, and post-lesson reflection. Results: Results highlight the ability for triads to conceptualize the integration of STEM concepts but also the challenge to sustain the integration of STEM concepts across phases of enactment. Conclusions: The need to support teacher learning of STEM content and pedagogical practices for integration are discussed.