While calls have been made for a multi/plural turn in Applied Linguistics, there remains a paucity of research investigating instruction that addresses the turn and its effects on student learning compared with monolingual one-language-only instruction. This study examines the effects of plurilingual instruction on students' plurilingual and pluricultural competence (PPC) relative to monolingual English-only instruction. Moreover, it investigates potential additional affordances. Seven teachers in an English for Academic Purposes (EAP) program in a Canadian university taught two intact groups for four months: treatment (plurilingual instruction, n = 79) and comparison (monolingual instruction, n = 50) groups. Results from "pre"- and "post"-tests of the PPC scale show that students in the treatment group had higher PPC levels over time relative to students in the comparison group. Moreover, analyses of diaries and focus groups with students in the treatment group show that plurilingual instruction offers affordances such as cognition, empathy, and criticality. These results are significant as they suggest that plurilingual instruction may be more effective than monolingual instruction in the development of PPC and it offers several additional affordances.