The study has addressed the critical role of using the mother tongue in the classroom for enhanced development of the English language. Despite the recognition of the critical role of first language (L1) in second language development, there is no clear guidance on how and when to use it. Teachers in Kenya lack clear guidance on how to develop learners’ mastery of the English language using leaners' mother tongue. Mastery of the English language has been a challenge to most of the learners who learn it as a second language. This may be attributed to a lack of proper guidance on the implementation of the language policy in Kenyan schools. The current study was undertaken to establish practised translanguaging during English language lessons and its implication on English language development. This was achieved by establishing how teachers used their mother tongue during the English language lesson and its implication. The study was guided by Communicative Language Theory (CLT) which emphasizes the transactional and functional roles of the language. This theory guided the evaluation of how teachers of English used learners’ mother tongue to teach English language concepts as well as interact with learners during the lessons. Three public primary schools in Kasarani Sub County in Nairobi County participated in the study. Audio-video recording supplemented by observation was the data collection method. Findings indicated that teachers used their mother tongue while explaining the meaning of words, paraphrasing sentences, and evaluating the understanding of a concept. Consequently, learners understood the concepts and improved their performance. However, teachers lacked clear guidance on how to use the mother tongue, which affects the positive impact of using the mother tongue. The study recommends that teachers be offered in-service courses on the effective use of translanguaging practice. The study adds knowledge of the existing theories on second language development.