The Zimbabwean Education Act of 1987 stated that English was the official language of learning and teaching (LoLT) from grade four upwards. From grade three downwards, the mother tongue was to be used. That Education Act was later amended in 2006, to extend the use of the mother tongue up to grade seven. As a college lecturer, I have observed that there is tension between policy and practice. English and indigenous languages are vying for supremacy as the LoLT from as early as the Early Childhood Development (ECD) level. For the majority of these learners, English is a second language. This research aims to investigate problems emanating from the use of English as a second language (ESL) in learning and teaching Environmental Science (ES) at primary school level. Its objectives are to investigate the usefulness of the language policy currently in use in Zimbabwe as well as to investigate empirically, how grades four to seven teachers and their pupils communicate in class during ES lessons; and identify problems resulting from the use of ESL during ES lessons at primary school level and suggest solutions to these problems. I purposively chose ES because I developed interest in that subject when I taught it at college level where I observed many students teaching it for almost three decades. Most of the pupils these students taught struggled to communicate in ESL. My research was not intended to test existing theory. Therefore I chose an inductive (qualitative) approach. I adopted the phenomenological case study in which I collected data from the natural setting, namely: three purposively selected primary schools. I did my pilot study at the fourth school. I used four methods of data collection, namely: direct observation, in-depth interviews, focus group discussions and document analysis. The participants were grades four to seven teachers and their pupils. Findings of this study show that pupils were not willing to participate in class oral discourse. When teachers asked questions, pupils usually gave one-word answers. Teachers and pupils spoke the same first language (L1). So, when they failed to express themselves coherently in English, they code-switched to their L1. When that happened, most of the pupils were eager to talk. They gave correct responses in their L1. Group discussions were very lively when they were held in the pupils’ L1. But when teachers instructed the pupils to discuss in English, many pupils were silenced because of their limited English proficiency (LEP). It was very evident that ESL was a barrier to the learning of ES for many learners. Pupils faced conceptual and communication problems because most of them were not yet proficient enough to use ESL effectively to learn ES. Participants welcomed code-switching to L1 as a solution to their limited English proficiency. / Educational Studies / D. Phil. (Education)