The purpose of this study is to reveal effectiveness and challenges of interactive learning in music lesson, through a music lesson practice adopting different graders' interaction. As a case study, this study focuses on the 4th graders' acculturation through the interaction in Koto lesson with 8th grade students in junior high school. Findings reveal that the interaction is most effective in raising pupils' consciousness and skill for ensemble. Most of the 4th graders take particular note of the sound overlapping with that of 8th graders. They can feel that their tone color was changed by overlapping with 8th graders' musical performance and they can improve their individual musical skill. Interactive learning enables pupils to become aware of these results mentioned above. Based on results, challenges for the future reveal that the place for Koto performance is limited and we need to arrange the topic considering that different schools have different time schedule. Planning the interactive and collaborative learning not in terms of curriculum, but in the level of subject lessons, there is a need to find out and deal with more appropriate challenges.