The aim of this study is to determine 6th, 7th and 8th grade students' indicators of knowledge of light concept through peer tutoring and examining peer tutoring applications. Multiple case study method was used in the research. As tutors, five students were chosen from 6th, 7th and 8th grades were participated in the study. As tutees, five students from 5th grade were selected. While peer tutoring was held, all sessions were videotaped. Videotapes were transcript and analyzed with Nvivo 9 software. Doing descriptive analysis, at first open coding was made and then categories were formed from these codes. The categories generated from codes were students' indicators of knowledge of light concepts, materials used in the process and learning channels. It has been seen that mainly tutors relate light with sight; reflection is idiosyncratic for shiny things and law of reflection is applicable only in diffuse reflection. It has revealed daily life experiences and textbooks were quite effective for tutors to construct concepts. In that case, it was suggested classroom activities and textbooks should be arranged for students to understand and form concepts aright.