The data was collected using a mixed method study of convergent parallel design, conducted using classroom observations, interviews and questionnaires to triangulate the data obtained from the three Premier Polytechnics in Malaysia, which involved nine lecturers and 183 students. The data is useful in focussing on the structure that normally occurs whenever code-switching happens and to test on how effective it is in the learning of English. Further research could also be based on these data as to identify the potential functions of code-switching and its contribution towards the language policy in Malaysia as reference to other countries too. It will provide an understanding of patterns and reasons for code-switching and subsequently offer insights into the use of code-switching as an effective language teaching and learning strategy.