I argue in this article that identity as a mathematical thinker develops through self-directed learning within a supportive community of practice. The dynamic nature of identity as a mathematical thinker is illustrated by considering the experiences of primary pre-service teachers who undertook a mathematics and technology subject in their undergraduate education degree. The pre-service teachers developed their identity as self-regulating learners through setting goals, planning, organising, recording, self-evaluating, and structuring their learning environment. Affective issues, such as resilience, confidence, and ownership, were also significant in identity formation. The mathematical social context provided by the tutorial group and use of technology impacted on self-regulation and social identity and hence on pre-service teachers' identity as mathematical thinkers. (Contains 2 figures.)