This study describes how a secondary school teacher in Trinidad and Tobago implemented opportunities for reasoning and proof in Geometry. Data were collected via teaching observations, teacher interviews, audio, and video recording. The analysis of the data suggested that the teacher used open-ended questioning, revoicing, group work, and problem-based learning to motivate students to explain their thinking and engage in mathematical experiences with pattern identification, conjecturing, and proof-construction. The teacher also created a social constructivist environment for students' engagement with reasoning and proof. Overall, the teacher's instructional practices seemed to align with the reformers' vision for mathematics instruction. The findings of this study can help reformers and policy makers understand the interplay between reform-based policies and actual classroom instruction.