The results from the 2015 Trends in International Mathematics and Science Study (TIMSS) point to a clear relationship between language and performance in Mathematics and Science achievement worldwide. Using countryspecific data from the Grade 5 and 9 study, we examine this relationship in South Africa. Learners’ achievement can be impacted by a wide range of factors. Some factors have particularly powerful effects in certain countries, due to the prevailing context. In the South African context, language and literacy are a crucial part of explaining learner achievement. The language used in South African education is a highly contentious issue due to its previous use as an exclusion tool under the Apartheid government.