ABSTRACT The study explored the challenges of using English as a medium of instruction in the upper part of primary schools in rural Uganda. The sample consisted of the head teacher; pupils and teachers of upper primary school grades (five to seven), from one selected primary school in Mpigi district. The research questions used were: How do teachers use English as a medium of instruction in the upper part of primary schools in Mpigi district? How are teachers facilitated by the government in using English as a medium of instruction in the upper part of primary schools in Mpigi district? How does English as a medium of instruction affect pupils’ academic performance in the upper part of primary schools in Mpigi district? The study adopted a qualitative design. Tn-depth interviews were conducted with selected pupils, teachers and the head teacher. Classroom observations were also conducted as a support method with teachers of English, Mathematics, Basic science and health education as well as social studies, the examinable subjects in Ugandan primary schools. In addition, relevant policy documents were reviewed. The findings revealed that pupils and teachers in the rural primary schools experience dilemmas and tension, in the teaching and learning process, partly owing to language in education policy. Implications for the teaching in either local language or English as a medium of instruction were discussed and a number of challenges in using English as a medium of instruction were revealed, which consequently had a negative effect on pupils’ academic performance. This proved that pupils understand better when they are taught in a familiar language (local languages) than when they are taught in a non- familiar language (English), as it has been claimed by several intellectuals in the same field of study.