This study uses activity theory to examine collaboration between graduate students (in-service teachers) serving as literacy coaches and undergraduate students (pre-service teachers) functioning as tutors in a university reading clinic. The participants tutored students in grades first through sixth for seven weeks. The purpose of the study was to understand how this experience shaped the pre-service teachers' pedagogical content knowledge. The data showed that through various types of collaboration, the participants' knowledge of struggling readers grew. Implications include creating and examining additional "spaces" for pre-service and in-service teachers to collaborate in order to strengthen pedagogical content knowledge.