Educational digital games are often complex problem-solving experiences that can facilitate systematic comprehension. However, empirical studies of digital game based learning (DGBL) have found mixed results regarding DGBL's effect in improving comprehension. While learners generally enjoyed the DGBL learning experience, they often failed to comprehend the underlying message and construct knowledge. One possible explanation for the mixed results is that DGBL comprehension is moderated by individual differences in working memory and gaming expertise (knowledge, skills). Due to the procedural nature of communication in game design, learning from digital games requires processing multiple interacting elements within one's working memory. The amount of available working memory that can be allocated to processing the "educational messages" is affected by the learner's expertise about the game mechanics, along with the structure of the game design. This study seeks to investigate how working memory capacity and gaming skill expertise interact with game scaffolding design to influence attention and comprehension. Two specific game scaffolding designs--"content-knowledge scaffolding" and "gaming-skill scaffolding" are examined in this study. The two designs are aimed to support learning by reducing the amount of efforts that players need to exert to figure out how to play the game, thus reducing the demand on their working memory and freeing up working memory for comprehension. But some studies have shown that learners' expertise level also moderates the effect of these designs. Learners with more expertise do not benefit from scaffolding--a phenomenon known as "expertise-reversal effect" or "reverse cohesion effect." This study has three goals: (1) to examine the influence of individual working memory capacity and gaming expertise on attention and comprehension in the context of digital games; (2) to examine the effect of scaffolding designs on attention and comprehension with regards to working memory and expertise; and (3) to examine competing explanations from the expertise-reversal effect and the reverse-cohesion effect. The findings showed that gaming expertise significantly predicts attention when the player can recognize the game design (the game mechanics) as within their gaming expertise domain. Consistent with the expertise reversal effect and the reverse cohesion effect, players with higher gaming-skill expertise paid more attention to the gaming-skill scaffolding design. However, the findings suggest that gaming-skill experts and non-experts focused their attention on different aspects of the game. Working memory capacity and attention only predicted comprehension for learners with lower gaming-skill expertise. Working memory capacity and attention did not predict comprehension for learners with higher gaming-skill expertise. The gaming-skill scaffolding design was effective in mitigating the gap between learners with high and low gaming-skill expertise. However the content-knowledge scaffolding widened the gap between learners with relative high and low prior content knowledge. The study argues that skill-based scaffolding can improve comprehension for non-experts in the context of digital game based learning. But whether scaffolding helps or harms comprehension for gaming experts depends on if the design activates retrieval of expert mental models and whether the game's narrative is closely aligned with its underlying messages. [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.]