This paper reports on a highly-structured Mathematics-Science Partnership (MSP) professional development (PD) program focused on the integration of science, technology, engineering, arts, and mathematics (STEAM) in elementary mathematics and science. With a support system including higher education STEAM education and content faculty, community informal learning partners, an external evaluation team, school administrators, and expert STEAM teachers, twenty-five teachers and five STEAM instructional coaches met together for whole-group PD as they developed and then implemented integrated STEAM problem-based inquiries in their classrooms. This paper describes how the PrimeD framework (Rakes, Bush, Ronau, Mohr-Schroeder, & Saderholm, 2017; Saderholm, Ronau, Rakes, Bush, & Mohr-Schroeder, 2017) guided the STEAM PD program through a collaborative and reflective process.