1. Build new knowledge by comparison. The written calculation of multiplying three digits by two digits is taught on the basis that students learn to multiply two digits by two digits. Compared with multiplying two digits by two digits, the arithmetic and algorithm are exactly the same. The key to the teaching of this course is how to guide students to transfer the arithmetic sum algorithm of multiplying two digits by two digits to multiplying three digits by two digits. Therefore, the design of this course is not to treat three digits multiplied by two digits in isolation, but to focus on how to let students learn to calculate three digits multiplied by two digits in written form, but to help students form written calculation skills and build a knowledge network by comparing old and new knowledge. In teaching, first, through the comparison of two different review questions, arouse students' existing knowledge and experience, summarize and sort out what they have learned, and at the same time make full preparations for new teaching. On this basis, let students try to calculate 144× 15 independently. On the basis of existing knowledge and experience, students have successfully migrated the written calculation method of multiplying two digits by two digits to the written calculation method of multiplying three digits by two digits, and guided them to understand the arithmetic of multiplying three digits by two digits in combination with the actual situation, making the abstract arithmetic concrete and more convenient for students to understand and accept. At the same time, teaching is not only about how to calculate three digits multiplied by two digits, but also lets students compare the new knowledge with the original knowledge, and clarify the connection and difference between the old and new knowledge in the comparison. In the two comparisons, students' knowledge has been constantly reorganized, and the knowledge network has been continuously enriched and improved.

2. Raise awareness through comparison. In the writing practice of multiplying three digits by two digits, two problems should be paid attention to: one is that there is zero in the middle of the multiplier, and the other is the vertical calculation of multiplying two digits by three digits. When there is a zero multiplication in the middle of the teaching multiplier, let the students compare which topic multiplier is special, and then let the students compare why there is no zero in the middle of the multiplier with two digits of 6 and zero in the middle of the multiplier with ten digits of 2. Let students really master the correct calculation method. When teaching the vertical calculation of multiplying two digits by three digits, let the students compare which multiplication formula is special first, and then let them exchange different calculation methods. In the comparison, it is concluded that it is more convenient to exchange the positions of two multipliers when calculating similar problems vertically. This not only highlights the focus of this course, but also further improves the students' cognitive structure, which is conducive to students' reasonable and flexible calculation.