The call for K-12 schools to prepare all students for college and career is pressing, however, the gap between high school and college writing persists. Concurrent Enrollment (CE) composition programs are one vehicle to bridge that gap. This paper looks at participation in CE programs as a site for transformative professional development, analyzing teachers' learning and development in practice. Findings from a year-long qualitative case study of three focal teachers offer insight into how teachers learn when partnering across institutional settings to deliver a college composition curriculum. The complex description of three teachers' experiences in this paper offers implications for the design and practice of cross-institutional partnerships and for the study of learning that takes place within those partnerships.