This paper presents data collected as part of an intervention research project to develop exploratory talk and collaborative group work with six and seven year-old students in mathematics. A discursive approach was used to analyse and interpret variations in the way that three case-study teachers, involved in the project, managed the group work and developed the students' talk. Analysis suggested that the intervention required, not just a change in practice, also but a shift in ideologies for these teachers. Ideologies are seen as discourses that legitimate and maintain a social pattern, and the paper explores how a research-based intervention can create conflicts between researchers' and teachers' ideologies.