<p>While international literature indicates that students’ first language constitutes a great advantage in their learning, the system of education in Morocco is still monolingual and promotes the use of a single medium of instruction. This study examined the factors behind freshmen’s preference for a certain medium of instruction in learning science subjects and the obstacles they face with exclusive reliance on one medium. It employed a mixed-methods research design. 104 freshmen from three departments at the Faculty of Science were surveyed through a questionnaire and 24 of them were randomly selected to participate in semi-structured interviews. Correlation tests were used to examine the quantitative data, and thematic analysis was utilized to analyze the qualitative data. Findings indicated that a variety of factors, including students’ perception of the role their first language plays in facilitating the learning process, their language proficiency, and their use of different languages in other spheres of daily life accounted for their preference for a particular medium of instruction. Our findings suggest that adopting a multilingual approach to education that recognizes all languages as valuable resources for learning and embraces students’ multilingualism through the use of their first language alongside the medium of instruction would create an inclusive and enriched learning environment that promotes effective learning and cognitive development.</p>