This article examines how secondary English teachers who served as mentors' for preservice English teachers developed their pedagogical content knowledge (PCR) of literature discussions through participating in a cross-institutional teacher educator network. In particular, we document how the joint creation of dialogic space in the English Educators' Network provided a context within which the mentor teachers expanded their understandings of discussions from disparate kinds of classroom talk to a dialogic view of literature-based discussion involving the interaction of reader, text, and multiple worldviews. We explore two central dimensions of this work: (1) how shifts in university and school participants' discourse, affiliation, and participation supported and expanded mentors' thinking about discussions; and (2) the central role of boundary objects, shared texts, and conversational brokers in facilitating these shifts. We begin with a brief review of literature on PCR to highlight the need for more research on cross-institutional contexts as sites for mentor teacher learning.