Background: Our article argues that the role of translingual instruction in mathematics classrooms is under-recognised in South Africa, as policymakers, teacher educators, teachers, learners, and parents assume that mathematics is just about numbers and calculations and not language. This is despite findings on the value of using children's familiar language resources in MacDonald (1991), code-switching for meaning-making in mathematics and science learning by Setati et al. (2002) and Probyn (2015), and the findings by Mbude (2019) on using isiXhosa for boosting mathematical and science skills. Objectives: The main aim of our article is to examine the role of the Languaging-for-Learning (L4L) project in fostering 'supportive teacher dispositions' to translanguaging and bilingual and multilingual education. We will accomplish this aim through description and analysis of one Grade 8 and Grade 9 mathematics teacher and her learners who participated in the project. Method: The study is a qualitative and interpretive linguistic ethnographic case study of a Grade 8 and Grade 9 mathematics teacher. The researchers used ethnographic methods to collect data and primarily draw on data transcribed from one of the video recordings of a lesson, fieldnotes of their classroom observations and still photographs from their classroom visits and L4L workshops. They used discourse analysis to interpret the data. Results: The research findings point to the critical role that fostering supportive teacher dispositions to translanguaging can play in teacher development and in supporting learners' engagement and learning in multilingual mathematics classrooms. Contribution: Our contribution to the field has been in demonstrating pluriversality in mathematics classrooms, showing how translanguaging enhances meaning-making and participation and helps to give voice to learners. Conclusion: Having multilingual resources, collaboratively building knowledge and resources and team teaching with teachers played a role in supporting the teacher's development in pedagogical translanguaging.