This paper describes research into the beliefs and practices established over time by teachers, who had been engaged in an innovative "mathematical investigations" school program, based on the use of exploratory software. The theoretical framework perceives the teacher as an active mediator of innovation, constructing and reorganizing a personal pedagogy. Interview and detailed observational classroom data were collected and analyzed, synthesizing qualitative and quantitative interpretations of teachers' comments in the classroom. The results show that teachers refer to a variety of aspects of the learning situations in which they intervene rather than just the mathematical concepts and ideas. They adopt multiple roles in the classroom and are influenced by the values of the educational system. The ways in which these issues influence teaching and learning of the mathematical concepts at hand is considered. The nature of teacher beliefs and the ways in which they may influence their practice is questioned. (Contains 6 tables.)