The key objective of the 2015 revised national curriculum in South Korea is nurturing transformative and creative convergence talent of students. Home economics teachers in South Korea have tried to shift the empirical-rational science-based home economics instruction into critical science perspective-based home economics instruction so that learners can develop these competencies. To help with this change, this study aimed to reveal the process of a teacher's reflection to implement critical science perspective-based instruction and resolve the difficulties on the reasoning stage, which is a key course of the instruction. Action research as a qualitative research approach was conducted. For the analysis it employed materials such as instruction observation journals, teacher's reflection journals, student interview records etc. The study revealed that it needed the teacher's constant challenges and reflections on the thinking process for implementing critical science perspective-based instruction. Through the reflection, the teacher realized that she should break away from her teaching tendencies and her fixed ideas of pedagogy, which reflected the empirical-rational science-based perspective. Also, it found that the teacher should experience and get familiar with how to think at each stage of practical reasoning earlier than the students: Identifying concerns, understanding context of concerns, making and evaluating alternatives, setting valued ends, and making a judgment about action. Based on these findings, the proposals of developing teacher's communities, teacher training, and a national home economics curriculum are suggested.