Abstract Language is a recognised factor in the performance and learning of South African learners, the majority of whom are schooled in a language other than their mother tongue. In this paper, we interrogate grade 6 learners’ answers to 40 questions across the mathematics curriculum qualitatively. Learners from a stratified random sample of public schools in the Umgungundlovu district in KwaZulu-Natal were given a questionnaire on their personal circumstances and a test on mathematical knowledge, mostly from the grade 5 curriculum. They wrote the test at the beginning of grade 6 school year. A quantitative analysis of the results indicated that English home language learners can be expected to score 14.5 percentage points higher on the learner maths test than non-English home language learners, after socio-economic status has been accounted for. However, correlating the difficulty of the question formulation with learner performance did not show any significant correlations. In order to understand furth...