This study explores teachers' conceptions of STEM education at the beginning of an online graduate course for practicing PK-12 teachers (n=20). A grounded theory approach was used to analyze open-ended survey data and concept maps. Teachers in the study interpreted STEM teaching from either a disciplinary or an integrated perspective. Their conceptions of STEM education within their concept maps fell into one or more of six categories: (1) utilitarian; (2) acquisition of disciplinary knowledge; (3) activities and resources; (4) access to meaningful problem-solving experiences; (5) advocacy for systemic change; and (6) buzzwords. This study reveals the complexity of teachers' conceptions of STEM education as they prepare to integrate STEM in their classrooms. The use of concept maps as a formative assessment can better position teacher educators and professional developers to move teachers toward a more sustainable integrated perspective of STEM teaching.