In our action research projects as teacher educators, we focus on broadening preservice teachers' understandings about language diversity in mathematics classrooms, away from just improving students' fluency in the language of instruction. To undertake these projects, we developed a flexible analytical tool, for identifying those pedagogical practices which could be improved and so broaden pre-service teachers' understandings about language diversity. By documenting the development of the analytical tool, we provide insights into how action research projects can contribute to aims for social justice. Using data from a wider project, the analytical tool is discussed in regard to its possibilities for identifying practices that could be improved, its validity and reliability, and its potential for use in other action research projects.