One of the objectives of teaching English in primary schools in Kenya is to enable the learners to communicate fluently, independently and accurately. However, there has been a declining standard of performance in English at primary level which should worry many teachers and stakeholders in education sector. This study aimed to examine teacher factors that affect Second Language Acquisition and to determine ways of improving acquisition of English in primary schools. The study applied Krashen’s theory of Second Language Acquisition and employed descriptive survey research design. Data was collected using questionnaires and interview schedules. The findings of the study show that personal factors such as motivation and attitude of the teacher appear to be more significant factors in the acquisition of Second Language. The study also found that teacher training, climate of the classroom, school support and social environment are factors that may improve Second Language Learning. Therefore, teachers need training especially in Competence Based Curriculum. The government and educational policy-makers and practitioners should look for ways of improving teacher quality in L2, knowledge and pedagogical skills. It is hoped that the current study adds knowledge to the teaching and practice of SLA.