Background: Teachers' limiting conceptualizations of students influence students' learning opportunities. We analyze teachers' professional conversations to understand how dialogues can expand teachers' conceptualizations. Methods: We examine professional dialogues from nine whole-school intervention meetings. Drawing on discursive psychology and activity theoretical notions of learning the study conceptualizes teachers' collective assumptions as a lived ideology actively sustained by stabilization discourses. We analyze the discursive devices through which the teachers' talk about their students limits/expands their sense of what is possible in their teaching and their dialogic effects. Findings: Our analysis finds a range of discursive strategies that sustain or re-stabilize the lived ideology. Even when challenged by contrary evidence (e.g., surprises), dilemmatic tensions and reframing repair actions are found to close potential dialogic openings. Importantly, we identify a form of discourse that avoids immediate closure, characterized by sustained reflection on the students' challenges developing a need to change. We term this reflexive noticing: it is enabled through sustained puzzle, constructing dilemmas as origin of change and discursive consciousness of stabilization. Contribution: We illustrate why contrary evidence often fails to shift limiting conceptualizations about students and show the discursive mechanisms generating possibility knowledge. Implications for teacher learning are discussed.