Researchers have been drawing attention to the power of collegial interaction for teacher professional development for some time. Yet collegial interaction should not be taken as a perfect solution absent of any drawbacks. In this study, the author examines teachers' collective construction of students to examine whether counter-productive patterns were being developed. To this end, the author analyses transcripts from whole group discussions of a teacher study group in which secondary mathematics teachers in the US participated. Teachers more often positioned students as more incapable than capable of doing mathematics or of communicating mathematical ideas. In addition, they tended to reinforce such deficit-based positionings more often than ability-based positionings. In this study the author suggests that deficit-based positionings tend to restrict teachers from exploring possible teacher moves. This study provides an example of a counter-productive interaction pattern which teacher educators could use to prepare themselves for facilitating productive teachers' collegial interactions.