It is generally argued that the medium of instruction places constraints on the classroom practices of teachers because students usually do not have sufficient English language proficiency to cope with the learning though the medium of English. Consequently, teachers respond with a teacher-catered approach, which nourishes rote learning and students dependency on the teacher. With reference to the teaching and learning of science, linguistic constraints further hinder the amount of extended discourse, student centered constructivist approach of teaching, and the learning of science. This dissertation reports on the findings of a study conducted in a primary grade science classroom at a private English medium school in the context of Karachi. The purpose of the study was to investigate teachers' strategies to make primary school science content more accessible to the students with limited English proficiency. The study arrives at three major conclusions firstly, the teaching and learning of science through the medium of English in a context, where the medium of instruction is not the first language of the learner, puts the teacher in a complex situation. Secondly, in the course of classroom practice the use of vernacular language along with English as the medium of instruction emerged as an important strategy to facilitate students' learning of scientific content and English language development. Thirdly, the study indicated that there is a need to include language-related issues in science teacher education programmes. In addition, the study argues for the improvement of teachers' professional craft knowledge' through involving them in the process of reflection. Implications of the study together with specific areas recommended for further investigation are presented and discussed.