In post-apartheid South Africa, 11 languages, including English and indigenous languages, were given equal status as official languages. Yet, more than 25 years after democracy, Black parents still believe that their children's wealth and success depend on English, and therefore, send them to English-medium schools where they take English as a second language (ESL), known in South Africa as English First Additional Language (FAL). Many circumstances compel teachers to code-switch between English and learners' first language. In the study reported on here we explored the reasons behind teachers' code-switching in FAL classrooms in 4 rural high schools in KwaZulu-Natal, South Africa. Concept maps, open-ended questionnaires and open-ended telephone interviews were used to generate data. Findings indicate that FAL teachers use code-switching to clarify difficult concepts, enhance understanding of the content presented, and keep learners engaged during lessons. We argue that the use of learners' first language may be crucial in the teaching and learning of a second language.