Using a broad-based assessment for understanding what teachers learn in historic site-based professional development (HSBPD), this study follows 29 teachers from a HSBPD at Thomas Jefferson's Monticello to see how their work at historic sites affected their practice upon return to their classrooms. Influenced by the Interconnected Model of Teacher Growth and Complexity theory, this study considers the complex outcomes of teachers as individuals, professionals, and learners in communities of practice. Results explore a range of outcomes related to content, pedagogical content knowledge, working with peers, interactions with the historic site, and a willingness to reconsider historical information. The discussion offers a consideration of the network of HSBPDs as a cumulative system and the ways in which teachers' on-site work can deepen our understanding of working with complex historical sources and make larger curricular changes.