In elementary school, transformation of plane figures aims to cultivate a sense of space. Sliding, flipping, and rotating are the contents of plane figure transformations in elementary school curriculum. The purpose of this study was to elaborately investigate elementary school students' understanding of the transformation of plane figures. For this, the following research question had been set up: 1) Are there any differences in understanding the three kinds of transformations (sliding, flipping, rotating) according to objects and elements of transformation?; 2) What are the difficulties that elementary school students face when transforming plane figures? To find the answers to these questions, sixty items were developed and the tests were conducted with 427 3rd to 5th graders from 6 schools. The analysis results were as follows. Students in the 3rd to 5th graders showed a high level of overall understanding of the transformation of plane figures. Students’ degree of understanding was high in the order of sliding, flipping, and rotating. Excluding the sliding transformation, the degree of understanding of the transformation was found to be maintained or increased after learning. Compared to the sliding and flipping transformations, the rotating transformation ranked the lowest in students' understanding of the object and element at hand being transformed as it was found that the 3rd to 5th graders had an incomplete understanding of the rotating transformation. Based on these results, some ideas were proposed to improve teaching methods as well as future studies on the topic.

the sense of space, transformation of plane figures, movement of plane figures, sliding, flipping, rotating