The catalyst for the growth of Lesson Study in Brunei was the introduction of a new 21st-century national curriculum intended to change the paradigm for teaching and learning. Research supported by a grant from the Brunei Research Council provided an opportunity to study the potential, the challenges and the necessary conditions for successful implementation of what became known as 21CTL Lesson Study, with a sample of 150 teachers. The study showed that gaining insights into the different ways that their students experience and respond to learning activities and, from this, gaining insights into the different ways they may help students to learn, supports teacher change and results in teacher learning. It also revealed the challenges of 21CTL Lesson Study. First, there is a need to deepen teachers’ experience of teaching beyond surface approaches involving transmission of content. Second, there is the challenge of facilitating or coaching the Lesson Study group along a learning trajectory. Third, there is a need to ensure alignment between the curriculum content, assessment and the goals of the curriculum. Finally, there is the task of convincing all the stakeholders in a top-down education system that Lesson Study supports effective ongoing, collaborative professional development for teachers.