Lesson planning through backward design was introduced in the schools in one of the Dzongkhags in eastern Bhutan to enhance students' learning since 2017. This study was undertaken to find out the effectiveness of backward design lesson planning in teaching and learning physics. A qualitative case study approach implementing semi-structured interviews, classroom observation, and document analysis was used. A purposive sampling method was used to select eight physics teachers from four schools. The study found that lesson planning using backward design significantly influences students' understanding of the concept and promotes purposeful classroom engagement through realistic classroom learning. As the assessment is planned separately in this design, it provided teachers with an improved understanding of students' learning, the achievement of learning standards and, subsequently, scaffolding them to achieve greater learning performance. The other benefits include improved academic achievement and increased confidence of teachers. Some challenges were limited evidence of transferring students' learning to their everyday lives; more time requirements in the planning phase; teachers' limited knowledge in setting instructional goals; and developing reliable assessment tools and essential questions. This study recommends conducting similar studies in other subject areas involving more participants to offer richer perspectives on the effectiveness of the backward design.