Purpose of the study: The purpose of the study is to investigate Mathematics and Science elementary school teachers' perceptions of using English as a medium of instruction in the United Arab Emirates (UAE) primary schools. Methodology: This research utilized an explanatory sequential mixed-methods design. The first phase of the research featured self-reporting by means of a questionnaire for elementary teachers (n=117), and the second phase used qualitative data by means of focus-group interviews (n=15). Main Findings: The results revealed that there is consensus among Mathematics and Science teachers that students' performance and achievements will benefit from the students' native language (Arabic) when used. Additionally, the teachers expressed that the students' low English proficiency embedded their understanding of Mathematics and Science concepts. Moreover, teachers indicated that they spend considerable class time teaching English instead of Mathematics and Science concepts. Applications of this study: This study is intended to portray teachers' perspectives on using English as a medium of instruction in the UAE elementary schools. It is hoped that the findings of the study may have implications for teachers, curriculum designers, and policymakers. Novelty/Originality of this study: In the context of the UAE, studies involving the investigation of using English as a medium of instruction were focused mainly on higher education. Thus, this study has the potential to fill an important gap by extending the research to include teachers an d students in elementary school and beyond.