Background: Many South African children attend African language medium of instruction (MOI) schools, learn English as an additional language and switch to English MOI three years later. There is still much to be researched about how a child’s first and second language literacy develops over time in South Africa. Aim: This study aims to outline the first and second language skills at the start of Grade 1, which are associated with English Second Language literacy at the end of Grade 1 through the use of a longitudinal design. Setting: Data was collected from 80 predominantly rural no-fee isiZulu and Siswati MOI schools in Mpumalanga. Methods: A total of 1347 learners were randomly selected from these schools and were individually assessed on various first language (isiZulu or Siswati) and English skills at the start and end of Grade 1. Results: The data show that learners begin school with varying first and second language oral language proficiency levels, and most learners are pre-literate. Decoding skills improved over the year, but 45.7% and 35% of learners were still unable to read a first language or English word correctly in 1 min. Conclusion: The data confirm the importance of first language phonological awareness and letter–sound knowledge for later word-reading abilities in isiZulu, Siswati and English, as well as their importance for English spelling. The study highlights the importance of the systematic development of English oral proficiency during the Foundation Phase especially for rural children who are not exposed to English in their communities.