Abstract: Medium of instruction is expected to influence academic performance of deaf students in sciences. For many years the debate of which mode of instruction to be used has remained to be a controversy between oral versus manual methods of instruction. Therefore, the current study sought to find out whether the medium of instruction influences the academic performance in sciences of deaf students at Ngala School for the Deaf in Nakuru County, Kenya. The study adopted descriptive research design. The study target population was 472 respondents at Ngala secondary school of the deaf. The quantitative data was presented using percentages, frequency tables and charts. The study results revealed that although varieties of communication approaches were being used by teachers, which were not limited to Sign Language, SEE, Bilingual Communication, Code Switching and Oral Communication, more than half of teachers were not fluent in Sign Language, Code Switching and Bilingual Communication approaches. Many teachers exhibited insufficient expressive and receptive skills. The study concluded that many teachers have difficulties in using KSL, Code Switching and Bilingual Communication. This has made it difficult for teachers to have a smooth interaction with the students in class. The study recommended that teachers should be exposed on in-service programs to enable them have skills in Total Communication as a philosophy for teaching deaf learners.