The purpose of the qualitative phenomenological study was to explore the perceptions, beliefs, and assumptions of elementary schoolteachers related to implementing the International Baccalaureate Primary Years Programme (IB PYP). Semistructured qualitative interviews were conducted with 17 PYP teachers in a private school in a large urban center in central Canada. The study involved answering two research questions. R1 asked the following: What conceptual changes do primary schoolteachers experience in the process of adopting the IB PYP? R2 was as follows: What are the elementary schoolteachers’ perceptions of the implementation of the IB PYP? The modified van Kaam method of analysis put forward by Moustakas (1994) was used to analyze the data. Eight themes emerged from the data analysis. Four key themes (change of thinking, instructional practices, teacher openness, and time) addressed R1, and four key themes (dialogue collaboration, professional development, school leadership, and school structure) addressed R2. Implications for schoolteachers included collaborating with colleagues within the school and in the larger educational community, including online forums and involvement in ongoing professional development. Implications for school leaders implementing a new reform included ensuring professional dialogue and collaborative planning occurred within the regular school schedule, providing ongoing professional development for all PYP teachers, allowing time for teachers to grapple with a new philosophy and to experiment with the reform in the classroom, establishing a school culture that supports and sustains change; and providing literature on the new reform that translates academic theory into practical understandable terminology.