Although recent calls have been made for a plurilingual shift in language learning, particularly in countries with linguistically and culturally diverse populations, teachers are still unsure about how to apply plurilingualism in the classroom. There remains a paucity of studies investigating the disconnect between the theory and implementation of the plurilingual shift. This quasi-experimental study addressed these challenges by implementing plurilingual instruction in one English language program in a Canadian university and examining teachers' perceptions of this type of instruction compared to English-only. Seven teachers, all co-researchers of the study, taught two groups of students with different approaches: One group received plurilingual instruction, and the other group received English-only instruction. A deductive analysis of semistructured interviews with the teachers and an inductive analysis of classroom observations were conducted. Results show several affordances of plurilingual instruction, such as engaging students in language learning, advancing agentive power, and developing a safe space. Moreover, although none of the teachers had received training in plurilingualism, they unanimously reported preference for plurilingual instruction. Challenges resulted mainly from teachers' history with the English-only teaching tradition. This study is significant because it pioneered research aiming to bridge the gap between the theory and practice of plurilingualism, contributing pedagogical directions in TESOL.