◆ Typical wrong questions:
Title: Fill in the appropriate length unit.
The height of the soda bottle is about 2 ()
One carriage of the train is 12 ()
Student misunderstanding: the height of soda bottle is about 2 (cm)
The length of the train car is 12 (decimeter).
◆ Cause analysis:
1. The representation of "life prototype" in children's minds is not very clear. During the interview, it was found that some students said that they had never seen a train, and some students were not very clear about the train carriages. It can be seen that some of our students have little real life experience, which leads to mistakes.
2. The establishment of length unit representation cannot be closely related to the objects in life.
Although students have perceived the unit of length in their minds and established the length representations of decimeter, millimeter, meter and centimeter, most students only stay on the length representations of 1m, 1cm, 1cm and1mm. When they apply this knowledge to the length of real objects, they lack strategies to solve these problems, and they can't be closely integrated with real life.
3. The method and ability to estimate the length of an object are not strong.
◆ Teaching suggestions:
1. In classroom teaching, we need more time for students to fully move and measure the surrounding objects besides helping students to establish the representation of the length of decimeter, millimeter, meter and centimeter. We can measure our math books, desks, chairs, blackboards and so on in the classroom. The more we perceive, the better. Ask the students to establish some basic concepts about the length of articles, such as: the pencil box is about 2 minutes long and the CD is about 650 thick.
2. Guide students to use the length of some familiar life prototypes as a reference, and learn to use the length unit accurately through strokes, comparison and reflection. If the height of the soda bottle filled by students is about 2 (cm), students can be guided to make a gesture. 2 cm is only about the width of two fingernails. The soda bottle is about 2 cm high, which is obviously wrong. The height of the soda bottle is similar to that of the pencil case. For a train car with a length of 12 (decimeter), guide students to imagine how many people can sit in a train car with only 1 meter. I believe that after guiding students to compare and reflect in this way, they will definitely choose the right unit.
3. Pay attention to the cultivation of children's estimation methods and estimation ability.
(1) Provide students with more exercises of estimating first and then measuring, so that students can compare the differences between the estimated results and the measured results, thus gradually correcting their own estimation strategies.
(2) Give full play to students' concept of space, guide students to imagine the length of objects, such as the height of houses and trees, and set some realistic, meaningful and challenging realistic estimation contents.