Informed citizenship in the 21st Century requires individuals to be numerate. In Australia, all teachers are expected to attend to numeracy inherent in the subjects they teach. Many teachers, however, find this approach challenging and may not see potential benefits for subject learning. Drawing on lesson vignettes and post-lesson interviews, a conceptual approach based on Wenger's communities of practice was used to analyse the use of "boundary objects" by four secondary history teachers. Their use of boundary objects was categorised by their attention to the "contextual" and "mathematical" meanings of the artefact they used. Findings suggest that there is potential for teachers to concurrently enhance subject learning and develop students' numeracy capabilities if they attend to both the "contextual" and "mathematical" meanings of the boundary objects they use. Research is needed into how numeracy is addressed in curriculum pedagogy courses. One aspect worthy of investigation is how boundary objects can be used effectively in subjects across the curriculum to enhance subject learning and promote numeracy development.