After-class reflection: The teaching of "What is circumference" follows the new concept of curriculum reform, and provides students with sufficient learning time and space through hands-on operation, cooperation and communication, and independent inquiry. Teachers' teaching ideas, teaching consciousness, teaching ideas and teaching implementation are all based on students' future development. This lesson highlights the following characteristics: What is the perimeter? Teaching content Understand the teaching goal of perimeter 1, and combine specific things or figures to understand perimeter through observation, operation and other activities. 2. Be able to measure and calculate the perimeter of triangles, parallelograms, trapezoid and other figures. 3. In combination with specific situations, feel the close connection between the surroundings and real life. Teaching focuses on difficult points through activities such as observation and operation. Know the surrounding situation. Experience the meaning of perimeter. Prepare leaves and wool for teaching. Teaching process 1. Know the surrounding situation. 1. Please draw the shape of a familiar leaf with one stroke. 2. Please report: What beautiful leaves did you draw? Can you work out the length of that leaf? Please have a try. Ask the students to measure a leaf individually or in groups. 4. Ask students to report the measurement methods and results. 5. Definition: Perimeter: The length of a figure in one week is called the perimeter of this figure. 2. Measure and calculate the perimeter of the graph. 1. Discussion: How many sides do you need to measure to get the perimeter of these figures? Why? 2. Student activities. 3. Report the results. 3. Are the perimeters of the two figures in each question the same? Why? 1, guide students to observe carefully and make judgments through measurement and movement. 2. Discuss and communicate in groups. 4. Reflective teaching. 1. Learn mathematics with real life. This lesson is based on the living materials familiar to students. At the beginning of the new lesson, a situation of small ants crawling on the edge of leaves and looking for the perimeter of surrounding objects was created. Let students establish the spatial concept of "one week" from many angles. We can combine children's cognitive characteristics, hobbies and psychological characteristics to design teaching content closely related to children's lives. Let students realize that mathematics comes from life and there is mathematics everywhere in life. In particular, let students draw the perimeter of leaves and measure the perimeter, so that students can master mathematics knowledge in the activities they are most interested in. Cultivate students' interest in learning mathematics. 2. Create a learning atmosphere of "independence, cooperation and inquiry". The teaching method has really changed the phenomenon that teachers ask questions, call individual students to answer, and teachers lead students away. It provides students with a broad space for autonomous learning and fully respects the main position of students' learning. The creation of various situations at the beginning of new courses not only provides students with opportunities for independent thinking, but also provides opportunities for cooperation and communication. Let them learn from each other in cooperation and exchange activities, and cultivate cooperation consciousness and inquiry ability. Students study in such an atmosphere, relaxed, happy and positive. 3. Emphasize the guidance of process and method. "Paying more attention to process than results" is another new concept of curriculum standards. When I introduced the concept of "perimeter", I didn't give out what the perimeter was prematurely, but let the students pass through the eyes, mouth, hands and eyes. Gradually understand the meaning of "perimeter". The learning of each knowledge point is to let students participate, experience and experience in person and fully experience the formation process of knowledge.