This paper examines middle school students’ process of understanding the concept of similarity. The purpose of this study is to create an effective teaching and learning model that can help students to gradually formalize the similarity concept. The model for learning similarity was developed based on Dienes’ Six-Stage Theory of Learning Mathematics and Choi’s Learning Level of Similarity. The model was applied to eight 7th grade students in Korea. As a result, students reached the third level of learning similarity, which is the stage of generalizing similar figures and their relationships as a reproduction on scale. Using various methods and tools, students discovered four main properties of similarity. Having further class discussion, students reduced those four properties down to two and kept those two properties as inherent properties of similarity. Only few researches have been done to develop learning model in reference to similarity that this research can provide an opportunity to observe the currently deficient areas of study. In addition, the research can provide an affective model of teaching similarity which also implies the need of further research in developing teaching and learning model for similarity.