This mixed methods study investigates the experiences, perceptions, and understanding of teacher leadership among PK-12 educators engaged in developing course content for a graduate certificate program. Data were gathered through surveys and interviews of the participants (n = 8) with diverse backgrounds and experiences. The findings provide insights into collaborative course design, highlighting diverse processes and challenges. The study emphasizes the value of collaboration and underscores professional development’s transformative potential in shaping beliefs about teacher leadership. These findings demonstrate how co-design fosters meaningful professional growth, deepens understanding of teacher leadership, and supports the development of leadership capacities.