“大树有多高”是一节实践活动课,是在学生掌握了比的相关知识,特别是学习了如何求比值之后安排的一个实践活动——测量树、旗杆、楼房的高度。这些物体都比较高,它们的高度很难用尺子直接度量,要通过“在同一地点,同时测得的竿长和影长的比值相等”的规律,间接获得。因此发现和应用这个规律是本次实践活动的重点。那么在发现和应用的过程中,我们应该着重帮助学生积累哪些活动经验?又如何引导学生发现规律,凸显“同时”“相等”等关键词, “How tall is a tree?” Is a practical activity class. It is a practical activity arranged after the students have mastered the ratio, in particular, how to find the ratio - measuring the height of the tree, the flagpole and the building. These objects are relatively high, their height is difficult to measure directly with a ruler, by “in the same place, at the same time measured the ratio of pole length and shadow length equal” rule, indirect access. Therefore, the discovery and application of this law is the focus of this practice. So in the process of discovery and application, we should focus on helping students to accumulate what activities experience? And how to guide students to discover the law, highlight “ ” “equal ” and other keywords,