Recent science education reform initiatives suggest that learning in science should be organized on the basis of scientists' actual practices including the development and use of models. In line with this, the current study adapted three types of modeling practices to teach two Korean 6th grade science classes the causes of the Earth's seasons. Specifically, the study aimed to identify the students' content-specific competencies and challenges based on fine-grained descriptions and analyses of two target groups' cases. Data included digital recordings of modeling-based science lessons in the two classes, the teacher's and students' artifacts, and interviews with the students. These multiple types of data were analyzed complementarily and qualitatively. It was revealed that the students had a competency in constructing models to generate the desired phenomenon (i.e., seasons). They had difficulty, however, in considering the tilt of the Earth's rotation axis as a cause of the seasons and in finding a proper way of representing the Sun's meridian altitude on a globe. But, when the students were helped and guided by the teacher and peers' interventions, they were able to revise their models in alignment with the scientific understanding of the seasons. Based on these findings, the teacher's pedagogical roles, which include using student competencies as resources, asking physical questions, and explicit guidance on experimentation skills, were recommended to support successful incorporations of modeling practices in the science classroom.