The study examined the effects of a new game mechanic on collaborative learning and mathematical discourse when playing a digital geometry puzzle game. For this study, two new versions of the game "Noobs vs. Leets" were developed. Both versions of the game teach the concepts of complementary and supplementary angles and the angle sum theorem of triangles. It was hypothesized that the version of the game that included a game mechanic that allow players to manipulate the angles, thus creating a more open-ended task, would be more intrinsically motivating, promote elaboration of the geometric concepts, and lead to greater learning gains. However, no differences were found between the two versions of the game in individual learning outcomes, the degree of mathematical elaboration by the pairs, or individual interest, effort or competence. Elaboration of the mathematical concepts in the pairs' discourse in the procedural game levels did predict individual procedural learning outcomes. Elaboration of reasoning did not, however, predict conceptual learning. To understand why no differences were found between the two versions of the game and why there was not a stronger link between elaborative reasoning and conceptual learning, eight representative pairs were chosen for more in-depth analysis. This analysis revealed that the pairs varied tremendously not only in their level of cognitive engagement but also in the quality of their social interactions. I conclude that successful collaborative learning with serious games requires not only careful consideration of how to align the game mechanics with the learning goals but also how to promote positive social rapport between players, as without this rapport, students will be unlikely to learn from one another or from the game. Future research on collaborative learning with digital games should examine not only the role of cognitive engagement in learning but also the role of social rapport. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]