While there is clear agreement that proficiency in the language of testing will influence educational outcomes, we know less about how this relationship is influenced by the socioeconomic status of learners and the schools they attend. Vijay Reddy and Jaqueline Harvey use grade 9 data from the 2019 Trends in International Mathematics and Science Study (TIMSS) to explore language dynamics in South Africa – nationally and in the Gauteng and Western Cape provinces. They look at how the different conditions influence science achievement, a subject where language skills are important.