How teachers perceived and experienced the implementation of a multilingual approach in their classrooms during the first year of implementation in Switzerland is poorly understood by policy makers and teachers. Findings from three pilot studies conducted before the implementation indicated that teachers had transferred only few aspects of the new multilingual approach into practice. Guided by constructivist learning and third language acquisition theories, this study explored how teachers perceived and experienced the implementation of the multilingual approach. A purposeful criterion sample of primary school English language teachers at Grade 5 who had completed a professional development program was targeted for this qualitative case study. Data were collected from interviews with and classroom observations of 8 teachers. Data analysis, conducted using initial and axial coding, revealed that teachers implemented the multilingual approach by closely following the instructions provided in a teacher manual, but needed more time to conceptualize the teaching and learning materials and to collaborate with other language teachers. These results prompted the development of a project to establish professional learning communities (PLCs). In PLCs, teachers will have time to engage in reflection, collaborate with colleagues, and strengthen teachers' classroom practices. This study has implications for social change as teachers who engage in collaboration with colleagues and reflective practice will positively affect student achievement. Students may be taught by teachers who have the knowledge, skills, and attitude required for a successful implementation of a multilingual approach.