Sign language is a system of communication that uses manual alphabets, hand gestures, facial expressions and finger spelling to convey meaning. It is used in communication as well as instructional language during teaching and learning process. However, there are variations in sign language worldwide and Kenya is no exception. The variations in sign language may affect academic performance among students in secondary school for the hearing impairment (HI). This study aimed at to identifying the sources of variations and the effects of variations on academic performance of students in HI schools. The study was guided by the ecological system theory of human development. Descriptive research design was employed. The target population of the study was 17 secondary schools for HI students, 589 form four students and 189 teachers. Two questionnaires were used, one for the teachers and the other for the HI students. A pilot study was conducted to assess the validity and reliability of research instruments. Data was analyzed descriptively with the help of SPSS version 25. The results were presented in tables and figures in form frequencies and percentages. Results from the respondents established that there were variations in the KSL which were brought about by the family background, the teachers’ interactions, peers and friends, the curriculum and also regional variations. It was also established that the variations affected the way the students receive and respond to various concepts during teaching and learning process which affected their academic performance. The study concluded that there were variations in the KSL, which influenced students’ academic performance. The researcher recommends that curriculum developers should consider these findings and align the curriculum to reduce variations. Curriculum developers to use the media to teach the community on the appropriate signs used for communication in Kenya more in service courses for the trained teachers to all other teachers to get the basic sign languages used in Kenya.