The teaching content of "knowing decimeter" is a knowledge point about length unit in the last semester of the third grade of mathematics published by People's Education Press. Students have studied meters, centimeters and millimeters, and decimeters are rarely used in real life, and students have little contact with them. Therefore, teachers are fully prepared according to the cognitive level and ability of junior two students in actual teaching, promote the mastery of knowledge and skills through various forms of teaching activities, and experience the fun of learning mathematics in the process of cooperation and exchange.

In today's teaching of decimeter, in the first link, students feel the practical significance of decimeter by measuring the length of desks. Students sometimes use rulers of different lengths. Because students always use 10 cm to estimate long objects when teaching centimeters, in fact, students still have some feelings about the length of 10 cm, but they just don't know that 10 cm is 1 decimeter. Therefore, students successfully established the concept of length of 1 decimeter through activities such as gesturing, looking around objects and estimating imagination. However, for four units of length, students still haven't practiced enough in the conversion between units. It is easy to make mistakes. It is necessary to strengthen practice and let children master the conversion between units in practice.

Due to the large class capacity, students are inconvenient to move in the process of personal measurement, which wastes a lot of time invisibly, resulting in a little nervous teaching progress. This point should be considered in advance in future teaching.