This study investigated the effects of cooperative group composition, student ability, and learning accountability on achievement, interaction, and instructional efficiency during computer-based instruction. A total of 125 sixth- and seventh-grade students were randomly assigned to heterogeneous or homogeneous dyads. Groups were designated as having either group or individual account-ability for mastery of lesson content. Cooperative dyads completed a tutorial on a novel symbolic mathematics topic, featuring basic symbol learning and application of the symbols. Indicators of ongoing cooperation were collected during instruction. Five days later, students completed a posttest. Low-ability students interacted more and completed the instruction more efficiently in heterogeneous than in homogeneous groups. High-ability students completed the instruction more efficiently in homogeneous than in heterogeneous groups. Cooperation was significantly related to achievement for heterogeneous ability groups, but not for either homogeneous high- or low-ability students.
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