This study examined factors that teachers say determine whether they modify new information about mathematics, mathematics learning, and mathematics teaching to fit their existing conceptions or whether they restructure their existing conceptions. Three female teachers (two sixth grade and one fifth grade) from a rural, public school participated in this study. All three teachers are currently participating in a research project which is disseminating new information about mathematics, mathematics learning, and mathematics teaching. There were no specific criteria used in the selection of the three teachers other than the fact that they had expressed an interest and willingness to participate in the study. Each teacher was observed teaching a mathematics lesson, and an interview was conducted following the observed lesson. Both the lessons and the interview sessions typically lasted one hour and were audio-recorded to secure a record for later analysis. Analysis of the interviews showed that while two teachers' existing conceptions of mathematics teaching underwent change as a result of their participation in the research project, one teacher's existing conceptions of mathematics teaching were preserved, seemingly as a result of her strongly held conceptions of mathematics and mathematics learning. The results seem to indicate that, though the role of the classroom as a learning environment and the role of reflection may be important to the change process, the role of the teacher is the most salient, since the teacher exercises considerable control over the decision of whether or not to implement change. (Contains 18 references.) (Author/ND)