本研究採取行動研究取向，由個案教師對臺中市某國小五年級一班學生34人，從事土石流教學；並探討學生對於山坡地保育與開發間所持立場抉擇與非形式推理。研究初始之第一行動循環，教師主張以土石流成因與影響等相關知識為重點從事教學，而後請學生表達第一次立場及理由。由於第一次選擇傾向於單一立場，於是在第二循環中乃再施以不同論點的文本閱讀，且由學生從事小組討論後，再請其表達第二次的立場與理由。繼之，在第三循環中設計並實施全班公聽會活動，使學生能充分溝通與分享意見後，陳述其第三次的立場與理由。本研究就三次立場及其理由變化進行分析，發現：學生針對山坡地開發議題，由一面倒傾向贊成不做開發的素樸立場，經不同論點的資訊介入後促使立場的轉換，並且激發出多樣的理由。透過公聽會活動分組及角色扮演，增加學生小組合作、分享報告與討論的機會。在研究全程中，並比較了全班學生對人類中心、生物中心與生態中心等環境倫理觀之變化。文末，就教學上的應用提出討論及建議。

This study, adopting action research approach, mainly focused on an in-service primary teacher to teach ＂mudslide＂ module in a grade-five class in central Taiwan. During the process, students' decision making, reasoning, and environmental ethical belief about the utilization of mountain or not were explored. The whole process consisted of three action research cycles. In the first cycle, the knowledge and naive information were introduced; then the students were asked to make their decisions with their justified reasons. In the second cycle, the students were given the counterpart information, and answered the questions as previously. Finally, a public hearing conference was held for students to present their information and opinions before the whole class. Then, the third decision and reasoning were made. The research data were analyzed based on statistics and qualitative ways. The findings included: in the beginning, almost all students advocated not to use mountain areas. After encountering with opposite opinions, a move toward the different end occurred and more reasons were aroused. The environmental ethic beliefs observed in the three cycles were compared. More than that, the discussion and implication were proposed.