This study examines the relationship between the functions and patterns of language choice in EFL classrooms in a Kuwaiti primary school. It applies the overall order model, specifically the medium of classroom interaction, to identify three patterns of language choice: an English monolingual medium, an Arabic monolingual medium and a bilingual medium. Then, an exploratory analysis of the relationship between specific patterns of language choice and broad functional categories of classroom code switching (CS) was conducted. No one to one relationship between a specific functional category and a specific pattern exists. One language pattern can serve different functions. From a detailed analysis, it is apparent that teachers in EFL classes try, as far as possible, to use the English monolingual medium to conduct pre-planned curriculum activities. However, when teachers and students departed from these prescribed activities, they used Arabic, either the Arabic monolingual medium or a bilingual medium, to serve different functions, such as accessing the curriculum, managing the classroom and establishing interpersonal relationships. On the other hand, the use of the prescribed medium (English monolingual) was never used to enhance interpersonal relationships.