【研究背景】20以内进退位加减法是计算中最基础也是最重要的内容,学生在计算的正确率与速度上都能达到比较高的要求。口算练习是学生每天必做的一项作业,但是训练形式往往比较单一。笔者调查发现,低年级学生课余的口算练习每天平均在60题以上,这样机械重复的 【Research Background】 Addition and Subtraction Addition and subtraction within 20 is the calculation of the most basic and most important content, the students in the calculation of the correct rate and speed can meet the relatively high requirements. Mouth arithmetic exercise is a daily job students must do, but training is often a single form. The author’s survey found that the lower-class students after-class exercise calculations a day on average more than 60 questions, so that mechanical repetition