教材呈现西师版小学数学关于“三角形边的关系”安排了一道例题的教学,一个课堂活动,三道练习题。其教学是在认识三角形有三条边、三个角、三个顶点以及三角形高的基础上对三角形特征的进一步认识。例3是把一根吸管任意剪成3段,看能不能围成1个三角形。通过让学生实际操作,发现有的学生所剪的吸管能围成三角形,有的不能围成三角形,引起认知冲突,采用对话框的形式提示:“我为什么就不 Textbook presented West division primary school mathematics on the ”triangle side of the relationship “ arranged a case of teaching, a class activity, three exercises. Its teaching is to recognize the triangle has three sides, three corners, three vertices and a triangle based on the further understanding of the characteristics of the triangle. Example 3 is a straw cut into three sections arbitrarily, see can not form a triangle. By allowing students to practice and found that some students cut straw can be formed into a triangle, and some can not form a triangle, causing cognitive conflicts, using the dialog box prompts: ”Why I do not