The purpose of the study was to explore the influence of teacher factors on mathematics performance among learners with hearing impairment in special secondary schools. The study was based on Vygotsky’s Zone of Proximal Development Theory and a Conceptual framework. The multiple case study research design was adopted in the study. The study was conducted in three secondary schools for the hearing impaired in the lake region (formerly Nyanza Province) in Kenya. The target population was 54 respondents that comprised of 3 principals, 12 Mathematics teachers, 9 Curriculum Support Officers 6 Parents representatives and 24 form 3 students. The study sample size was 47 respondents that comprised of 3 principals, 8 Mathematics teachers, 6 Curriculum Support Officers students, 6 Parents Teachers Association representatives and 24 form 3 students. Saturated, stratified and purposive sampling techniques were employed to pick out the sample. The research tools were interviews, observation, document analysis and Focus Group Discussion. The researcher collaborated and consulted with his supervisors and other expert lecturers in the school of education to validate the instruments. Trustworthiness of qualitative data was ensured using triangulation, thick description and member checking strategies. The qualitative data collected was analyzed using thematic analysis. On the concern about teacher factors influencing mathematics performance, the themes on teacher factors that emerged were: few mathematics teachers, gender of the teacher, teachers’ personality, age of the teacher, teacher competence, teachers’ professional experience, teachers’ knowledge and use of sign language, few teacher-learner consultations, teachers’ mode of delivery and inadequate teacher refresher courses. The study concluded that the themes on teacher factor were paramount in influencing mathematics performance among learners with hearing impairment. It was recommended that the government to staff special secondary schools for the deaf with teachers who are qualified in deaf education so as to improve performance in subjects like mathematics. A study on the influence of the degree of hearing impairment would expound the understanding of the current study.