This paper examines the impact of code-switching on the learning and teaching of Mathematics. The research was conducted in selected primary schools in O.R. Tambo Inland Education District in the Eastern Cape Province of South Africa. The researchers adopted a case-study research design. Four focus groups, each represented by six members, were used during data collection through semi-structured focus group interviews conducted face-to-face. Two groups were from rural-based schools and two groups were selected from urban-based schools. Purposive sampling was used to select participants with a focus on Mathematics grade six (6) teachers. The results show that code-switching is inevitable in teaching learners whose first or mother tongue is not English language when English language is used as the language of learning and teaching (LoLT). Secondly, code-switching is a useful and effective learning and teaching strategy for grade six (6) learners in Mathematics. The study recommends that teacher trainees should be introduced to a minimum of three (3) languages during their training in the teaching profession. In addition to making code-switching acceptable and official, Mathematics teachers should use it as a learning and teaching method or strategy. Keywords: Bilingualism, Code-switching, Learner Competence, Multi-cultural Classrooms