This qual-quan case study investigated the role of code-switching (CS) in education in four senior secondary schools in Botswana. CS is a communicative strategy used in many places, including Botswana, during formal and informal social occasions. CS also occurs in education; however, its occurrence is viewed as a somewhat problematical phenomenon – that it signals the speaker’s lack of proficiency in the Language of Learning and Teaching (LoLT). The study also investigated if CS in the classroom contravenes the country’s Language-in-Education Policy (LiEP), which states that English is the medium of instruction throughout the education system (Botswana Government White Paper No.2 of 1994). The study found that CS occurrence in teaching and learning has positive and negative educational effects. However, its use has adverse implications for the LiEP of Botswana. Consequently, recommendations are made on the effective use of CS and on the revision of the LiEP. The study is divided into nine chapters. Chapter One is the introduction and covers: Botswana’s language situation, including the status of English generally and in education in particular, the statement and analysis of the problem, research questions and the importance of the study. Chapter Two gives a comprehensive review of the literature on CS generally and CS in education in particular. The key words are: code-switching, code-mixing, borrowing, nonce-borrowing and re-borrowing / double-plural. Botswana’s LiEP is also discussed with respect to language planning, education and educational development. Chapter Three discusses the research design and the data-collection methods. These include: the research sites, sample selection and sampling procedures, data-collection instruments and their administration, and the independent and dependent variables used in data-collection. The importance of pre-testing the research instruments, ethical aspects observed and problems encountered during the data-collection stage are also highlighted. The role of the University of Pretoria’s Statistics Department is also explained. Hymes’ mnemonic of SPEAKING used in the analysis of the qualitative data is also described. Chapter Four presents the quantitative analysis of the respondents’ demographic details, and highlighting the differences and similarities identified. Chapters Five and Six present the results from the quantitative analysis of the teachers’ and learners’ data. The former presents the teachers’ evaluation of the learners’ language proficiency in class; the latter presents the learners’ subjective self-evaluation of their own English proficiency and their evaluation of teachers’ proficiency in English. Furthermore, both chapters respectively present the teachers and learners’ views on the role of English, Setswana and other indigenous languages in education as LoLT, and their attitude towards CS in education. The significance or the non-significance of the analyzed results is also presented. Chapter Seven presents the results from the qualitative analysis of the data (through the application of Hymes’ mnemonic of SPEAKING) obtained through lesson observations. Chapter Eight deals with the interpretation and discussion of the results through answering the main research questions. Chapter Nine presents the study’s summary, conclusions and recommendations on CS in the classroom and on Botswana’s LiEP. The study’s limitations and implications for further research are also discussed.