There is growing evidence of systematic underachievement of South African primary school learners in reading in English as the first additional language. There is a small but growing literature that provides insights, that is, causes, patterns and prevalence, into this phenomenon. Through a secondary analysis of a spelling component of a literacy test that was administered as an end-line assessment for a randomised control trial, this article provides new evidence for and insight into the patterns and prevalence of English language spelling errors made by Grade 4 second-language learners. The study specifically coded errors on four monosyllabic three-letter words for 2500 Grade 4 learners tested individually at the end of the second term in 2014. Three distinct linguistic error patterns were identified. The most frequent error patterns involved the incorrect use of the vowel grapheme, for example bed was spelled 'bad'. The second pattern related to common errors associated with the transfer of linguistic, orthographic patterns from the first language (isiZulu). The final pattern suggests that between 6% and 8% of learners were struggling to make the basic phoneme-grapheme connection. This pattern, however, would need to be confirmed with oral interviews. The implications of these error patterns are discussed.