As schools turn towards co-teaching models to implement inclusion practices (US Department of Education, 2010), teachers are increasingly being asked to operate with a co-teacher (Scruggs et al., 2007). However, most research on co-teaching remains at the survey level; it does not examine factors that may influence co-teaching relationships over time (Scruggs et al., 2007). This paper seeks to address that gap by examining the feedback a first and second year co-teacher give one another as they teach a high school mathematics course. The question under consideration is: what kinds of feedback may beginning co-teachers offer one another and how may it influence their classroom practice over time? The results of this work contribute to the broader body of co-teaching research by offering insights into a specific case of teacher collaboration. [For the complete proceedings, see ED606531.]