Early childhood classroom teachers are often left with little support and guidance as they assume responsibilities as mentor-teachers. The purpose of this collective case study was to explore how a hybrid community of practice comprised of four pre-K mentors and a university program coordinator supported the development of new understandings about how to effectively supervise preservice teachers. The evolution of collective and individual knowledge was chronicled through interviews, online discussions, face-to-face exchanges, and classroom observations. Data analyses included iterative cycles of coding, moving from open coding to process and pattern coding. Findings illustrate how mentors' processes of coming to know were developed within a complex web of relationships from which the dyadic roles and responsibilities as mentors of preservice teachers and teachers of young children were considered and negotiated. Implications include the need for more collaborative professional opportunities for pre-K mentors within school and university settings.