This study examined the psychological processes that promote active student participation in mixed-grade class activities within the framework of motivation to engage in cooperative learning and peer modeling. A questionnaire survey was conducted among the pupils of an elementary school, in which problem-solving-style mixed-grade class activities were conducted. Path analysis revealed that autonomous motivation to engage in cooperative learning inf luenced pupil perceptions of the structure of active participation in learning activities. Among third- and fourth-grade children, autonomous motivation to engage in cooperative learning reinforced perceptions of an active participation structure through dif ferent-grade peer modeling. Among f if th- and sixth-grade children, controlled motivation to engage in cooperative learning weakened perceptions of an active participation structure. These f indings underscore the important role of peer modeling and motivation in mixed-grade learning activities and suggest that the factors that facilitate active participation in mixed-grade class activities may dif fer across grades.