This study compares three pre-collegiate teacher professional learning and development (PLD) integrated science, technology, engineering, and mathematics (STEM) experiences framed in astronomy. The study is set in the western United States (USA) and involves 60 pre-collegiate teachers (in the USA these are K-12 teachers) over the course of three years (June 2014–May 2017). During the PLDs, astronomy acted as a vehicle for pre-collegiate STEM teachers to increase their STEM content knowledge as well as create and implement integrated STEM classroom lessons. The authors collected quantitative and qualitative data to address five research questions and embraced social constructionism as the theoretical framework. Findings show that STEM pre-collegiate teachers are largely engaged with integrated STEM PLD content and embrace astronomy content and authentic science. Importantly, they need time to practice, interpret, translate, and use the integrated STEM content in classroom lessons. Recommendations for PLD STEM teacher support are provided. Implications of this study are vast, as gaps in authentic science, utilizing astronomy, PLD structure, and STEM integration are ripe for exploration.