近年來的少子化現象，讓臺灣小型學校數逐年增加，班級人數過少，除了影響學生與同儕互動的機會，也限制教師教學策略的選用，跨年級教學是學校面對這種挑戰的對策之一。本文以一所在高年級自然領域實施跨年級教學的小學為研究對象，透過課室觀察、教師訪談和文件分析，探討國小跨年級自然教學實施差異化教學的行動歷程，並分析授課教師的協同合作方式。研究結論為：（一）在跨年級自然教學採取多層次的分組學習活動是差異化教學的可行策略；（二）提供教學鷹架可協助學生完成自主學習活動並培養自調學習能力；（三）採取教師協同教學模式有助於跨年級自然領域實施差異化教學。最後，依據研究結果，提出三項研究建議。

Recently, due to the declining birthrate, the number of mini-schools in Taiwan increases every year. Comparing to past classes, now both the chances for students interacting with peers and the options for teachers’ teaching strategies have been largely restricted due to fewer students in a class. As a result, the multi-grade teaching becomes one of the major strategies for these mini-schools in coping with such a challenge. This study, adopting a set of measures of classroom observation, interviews with teachers, and document analysis, explores the journey how a differentiated teaching has been applied to multi-grade science taught in an elementary school, with a further analysis on what patterns of collaboration conducted among the teachers. The participants include two teachers and 11 upper graders in a remote school. Three conclusions found are: (1) adopting the multiple-group learning activity in multi-grade science teaching is a practical teaching strategy for differentiated teaching; (2) providing a teaching scaffold can support students in completing self-learning activities and cultivating self-regulated learning ability; (3) adopting a collaborative teaching model could contribute to differentiated teaching in a multi-grade science teaching. Based on these results, three research implications are further suggested.