Early critical thinking and sustainability awareness development is crucial for equipping future generations to handle global issues in an increasingly complicated and interconnected society. This study examined how 9-year-old primary school students applied their knowledge through a collaborative Mystery assignment, demonstrating a Thinking Skill Learning Strategy within education for sustainable development. The Mystery Learning Strategy supported holistic and pluralistic educational approaches, fostering critical thinking, social interaction, and individual development within a socio-cultural framework. Inspired by lesson study principles and based on participatory observations, the findings revealed that while the Mystery approach is dynamic and engaging, it requires careful facilitation to be effective. The study demonstrated that collaboration and critical reasoning were fostered among students. By working in groups, sharing ideas, and building on one another's suggestions, students engaged in communication, active listening, and the integration of diverse perspectives. Future research could investigate the long-term effects of the mystery approach on developing critical thinking skills and enhancing sustainability awareness in younger students. [Note: The volume (15) shown in the header on the PDF is incorrect. The correct volume is 14.]