【问题缘起】本节课是北师大版小学数学一年级下册第一单元“加与减(一)”——“20以内退位减法”第四课时的内容。教材创设了学生开会的情境(如下图),涉及到参加会议的人数与会场椅子的把数之间比多少的问题,从而引出比较的必要性,并给出了三个问题:“每人坐1把椅子,够吗?”:“还缺几把椅子?”;“你能列式解决问题吗?下面的列式你同意吗?”。教学中,学生都知道椅子不够,并且知道还缺4把椅子,可是在 The origin of the problem This class is the first unit of the first grade undergraduate mathematics version of Beijing Normal University Edition “add and subtract (a) ” - “20 less abatement subtraction method ” the fourth class content. The textbook creates a scenario for student meetings (pictured below), which deals with the question of how much a person attending a conference might have compared with the number of chairs in a conference room, giving rise to the need for comparison and giving three questions: “Each person Do you have a chair, is it enough? ”:“ How many chairs are there? ”“ Can you solve the problem in a row? Do you agree with the following column? ” In the teaching, the students knew that the chair was not enough, and knew that they still lacked 4 chairs, but they were there