Numeracy is an integral part of subjects across the curriculum. If all teachers are able to identify and exploit the numeracy learning opportunities that exist in the subjects they teach, then students' numeracy capabilities along with learning in each subject is likely to be enhanced. This article builds on previous research where it was suggested that teacher identity could be used as the analytic lens to identify ways to support teachers to embed numeracy across the curriculum. The aim of this article is to propose a sociocultural approach that could be used to capture the situated and dynamic nature of a teacher's identity in this particular context. The case studies of two teachers are presented to illustrate how Valsiner's zone theory could be used to anticipate how this identity might develop over time and to design interventions to assist teachers to promote numeracy learning. Analysis of the two cases enabled the different ways needed to assist each teacher to be identified, thereby suggesting the potential of this approach for use in further research.