This study demonstrates a leadership professional development (PD) with a goal to build a coalition for attracting and retaining a diverse STEM teaching workforce in K-12 schools. In 2019, 111 participants of 21 teams from across the US participated in the leadership PD. Each team was comprised of 5-6 teachers and administrators representing their schools, districts, regions or states. The leadership PD enabled teams to share their problem of practice related to diversifying the teaching workforce and exchange ideas to resolve their challenges by working as a team with their matched mentor, who supported the group throughout the year. By the end of the 3-day workshop, each team developed a logic model that they could bring to their home school or district to take actions on promoting a diverse teaching workforce in their regions. In this study, we investigate the participants' attitudes and confidence toward the diversity in education; their thoughts about the leadership PD structure and their learning experiences; and the dynamics of an activity system that works to promote diversity in the teaching workforce, using the lens of the cultural-historical activity theory (CHAT).