Kenya has legislated a Language in Education (LiE) policy to use mother tongue in lower primary classes (class 1-3), yet the pupils in Tabaka Division of Kenya continue to perform poorly in national examinations. The purpose of this study was to investigate factors affecting teaching and learning in mother tongue in lower public primary schools in Kenya. The Chomsky’s theory of language acquisition was adopted. The study employed the sequential triangulation research design within the mixed methods approach. Questionnaires for teachers were used to collect quantitative data while qualitative data was collected using interview schedules, focus group discussions (FGDs) and observations. The validity of instruments was ensured by expert judgment by university lecturers while reliability was ensured by external consistency and a coefficient of r = 0.775. The target population comprised of 6000 pupils, 170 teachers, 17 head teachers, and 10 parents out of whom 90 pupils, 9 head teachers, 9 class three teachers, 10 parents and 1 Education Officer were sampled. Saturated sampling technique was used to select the head teachers, the primary schools, and class 3 teachers of lower primary, while simple random sampling was used to select the learners. Descriptive statistics was used to analyze quantitative data while interview data was analyzed using Thematic Analysis. The study reported that both teachers and learners had negative attitudes towards teaching and learning in mother tongue. The study recommended that relevant education players develop a curriculum which would result in the use of local languages as tools for economic empowerment and help change the attitudes of teachers, learners and parents towards teaching and learning in mother tongue.