Numeracy is identified in the Australian Curriculum as one of seven general capabilities that are to be developed across all curriculum areas making the development of student’s numeracy capabilities the responsibility of all teachers. As mathematics is the discipline that underpins numeracy teachers must be able to identify the mathematics inherent in their own learning area and design appropriate learning activities in the context of this learning area. If they are to do this they must see themselves not only as teachers of their own learning area but also as teachers of numeracy, in other words, develop an identity as a teacher of numeracy. An understanding of how teachers form and develop a numeracy teacher identity will assist in supporting them to develop effective strategies for numeracy learning in the context of their learning area. This paper extends a framework for numeracy teacher identity developed through a literature review of teacher identity and explores how the development of numeracy teacher identity can be investigated empirically. The numeracy teacher identity framework incorporates a knowledge domain, an affective domain, a social domain and a life history domain. Each of these domains includes a number of characteristics that interact to produce a teacher’s numeracy teacher identity. Arguing that knowledge of curriculum should be incorporated into the knowledge domain along with the characteristics of mathematics content knowledge and pedagogical content knowledge and explaining how characteristics of the life history domain influence the other domains extends the numeracy teacher identity framework. The paper argues that an understanding of how the characteristics identified in the numeracy teacher identity framework interact and contribute to the development of numeracy teacher identity can be gained through a sociocultural approach that uses an adaptation of Valsiner’s zone theory as the theoretical framework. The characteristics of the knowledge, affective, social and life history domains of the numeracy teacher identity framework are mapped onto the Zone of Proximal Development (ZPD), Zone of Free Movement (ZFM) and Zone of Promoted Action (ZPA). To illustrate how empirical data can be analysed through this theoretical framework two hypothetical case studies are described and the hypothetical data is mapped onto the ZPD, ZFM and ZPA to gain an understanding of each hypothetical teacher’s numeracy teacher identity.