In the context of the 2018 General Education Curriculum, which emphasizes the development of students’ qualities and competencies, developing subject-specific educational plans requires regular collaboration and reflection among teachers within professional groups. This paper presents the results of applying Lesson Study to the development of a Physics educational plan at Chu Van An High School, Dak Lak Province. A case study approach was adopted through two illustrative teaching cycles focusing on the topics “Wave Exercises” and “Light Interference.” The data included lesson plans, records of professional meetings, classroom observations, lesson videos, and feedback from participating teachers and school administrators. The results show that Lesson Study supports teachers in translating learning outcomes into learning activities and tasks, while enabling them to observe and analyze students’ learning processes to adjust teaching plans. Based on these findings, the study proposes a process for applying Lesson Study that is appropriate to the practical conditions of Vietnamese upper secondary schools.