How much is left is a conceptual lesson in Unit 3 of Senior One Mathematics-Cognitive Subtraction. Subtraction, like addition, has a large number of prototypes in life, such as remainder, reduction, comparison and so on. Although this course is the first time for students to contact subtraction, they often encounter these prototypes in real life, and they have initially felt that the phenomenon of "taking out or taking out one or more objects from a whole is decreasing" is still in the physical perception stage. The beginning of this lesson is to help students gradually understand the significance of subtraction, know which phenomena in life can be calculated by subtraction, and initially explore the calculation method of subtraction within 5.

In this teaching, I focused on the significance of subtraction, and the specific methods are as follows:

1, situational feeling-show two situational pictures, first guide the students to observe, and then ask: What are the pictures? Can you tell this story? First, organize students to communicate at the same table and tell stories at the same table, and then guide students to communicate in the whole class on the basis of deskmate communication. Students' language expression is relatively complete, such as: there are five apples on the tree, two apples are dropped, and there are three apples left on the tree; There used to be five pieces of cheese on the ground, and the mouse took two pieces, leaving three pieces of cheese on the ground. This kind of communication can make every student participate in it and perceive the meaning of subtraction in the process of narration.

2, physical operation-can you use a stick to put out the meaning in the picture? The first release of the stick is the teacher's narration and the student's operation. After the class is finished, invite another student to show it in front of the stage. With the foundation of the first time, let the students speak and swing the stick in the second time. Students are interested and willing to do it, and once again understand the significance of subtraction in the operation activities.

3. Symbolic expression-When exploring the calculation method of "How many pieces of cheese are left", I asked: Besides counting, can you draw a picture to show that there are three pieces of cheese left? The students can't wait to draw in their exercise books. Students choose all kinds of graphics, here are a few.

After students have experienced the significance of subtraction many times, I encourage students to try to express these two story situations with an expression, and students naturally write the subtraction expression 5-2=3. At this time, I will introduce the reading method of MINUS sign and expression, and guide students to talk about the meaning of each part of expression in combination with the situation map just now. Through the above links, students can experience a process from image to abstraction, which is in line with students' cognitive laws and the formation process of knowledge, so that students can easily and naturally understand the meaning of subtraction.