Emotion mediating educational outcomes has been recognized for decades. However, empirical experiments to test these predictions, particularly for climate change education, which is often mixed with various emotions, are rare. In this study, we conducted a two-week climate change education program with specific video clips designed to induce fear or hope in students to explore how emotions affect educational outcomes. The study involved 1,730 students from nine middle schools in three coastal cities (Xiamen, Shenzhen, and Ningbo) in China. The results demonstrated that emotional video clips are a successful stimulus for the target emotion. In the hope treatment group, emotion did not significantly affect the educational outcomes, as indicated by the limited change in students’ climate change involvement, self-efficiency, and mitigation behavior. However, in the fear treatment group, emotion significantly decelerated students’ change in mitigation behavior compared to the lecture-only group. These decelerated behaviors are mostly located at the behavior change of low carbon life. Based on the mediation analysis, both the hope group and lecture-only group had direct effects on climate change mitigation behavior, while the fear group only had an indirect effect on climate change behavior, mediated primarily by climate change involvement. The study thus highlighted that both negative and positive emotions should not indiscriminately used in climate change education programs to safeguard significant educational outcomes.