This study aimed to explore significant others, referring to the individuals who have effects on identity development, in mathematics teachers’ stories of teacher identity development. In line with this aim, five middle school mathematics teachers have been monitored in their last two years of the teacher education program and their first year of in-service teaching. The data were collected through a total of three interviews, each held at the end of the year. Analysis revealed that practicum teachers were one of the significant others in participants’ mathematics teacher identity development. Practicum teachers became role models for the participants in terms of pedagogical and mathematics teaching practices. Based on their observations of practicum teachers, they developed some intentions about how the relationship with students should be developed and which methods should be preferred while teaching mathematics.