“圆的周长”是苏教版国标本五年级下册的一个教学内容。教材是让学生在合作和交流中通过测量和计算推想出圆周长大约是圆直径的3倍多一些即圆周率,进而推导出圆的周长计算公式。例5的教学我是这样预设的:1.出示例5,指导读题。2.思考:你准备怎样来测量圆的周长?根据学生回答相机演示滚动法和绕线法。3.实验操作。每组分别用自己喜欢的方法测量事先准备好的3个直径不同的圆 “Circle perimeter ” is a teaching content of the fifth edition of the Soviet version version of the national standard. Textbook is to enable students in cooperation and exchange through measurement and calculation to figure out the circumference is about three times the diameter of the circle more than the number of the pi, and then derive the circle perimeter formula. Example 5 teaching I presumed this: 1. Example 5, guidance reading. 2. Thinking: How are you going to measure the circumference of the circle? Answer the camera demonstration based on the student’s roll and roll method. 3. Experimental operation. Each group, respectively, with their favorite method of measuring the prepared three different diameter circle