This paper presents an educational game in mathematics based on an apprenticeship model using a teachable agent, as well as an evaluative study of how the game affects (1) conceptual understanding and (2) attitudes towards mathematics. In addition, we discuss how collaborative and competitive affordances of the game may affect understanding and motivation. 19 students played the game in pairs once a week during math lessons for 7 weeks (the game-playing group) while another 19 students followed the regular curriculum (the control group). Math comprehension scores increased significantly for the game-playing group but not the control group (p < 0.05). However, there was no significant difference in attitude change between the two groups. Post hoc analyses indicated that game-playing primarily affected students' confidence in explaining math to a peer, but not their enjoyment of doing so. Collaborative and competitive activities seem to carry a strong motivational influence for students to play the game. © 2012 Association for Educational Communications and Technology.