Asynchronous online discussions have the potential to facilitate meaningful learning activities, such as ill-structured problem-solving, due to their asynchronicity and connectivity. However, the literature identifies two significant challenges in effectively supporting students' ill-structured problem-solving in these environments -- argumentation and social interactions. Although argumentation is critical for ill-structured problem-solving, students tend to avoid engaging in critical argumentation activities, such as generating rebuttals and counterarguments, to construct meaning in discussion forums. Similarly, social interactions are essential to ill-structured problem-solving, but students tend to display low levels of engagement in asynchronous online discussions. This study aimed to explore how these two critical components of problem-solving can be supported in asynchronous online discussions using question prompt-based argumentation scaffolds in combination with social presence enhancement strategies. The primary focus was to compare the differential effects of question prompts alone and the combination of question prompts with social presence enhancement prompts on students' argumentation behaviors, problem-solving processes during discussions, and post-test problem-solving performance. This study randomly assigned 44 students to three conditions (control, question prompt-based, and question prompt with social presence enhancement) to analyze their argumentation behaviors, problem-solving processes, and problem-solving performance in asynchronous online discussions. The findings reveal that: (1) lower level interactive argumentation behaviors dominate over higher level interactive ones; (2) students focus more on identifying problem representations and generating solutions than on justifying and evaluating them; (3) there is no significant difference in argumentation behaviors and problem-solving processes in asynchronous online discussions across the conditions. However, students who received both the question prompt scaffolds and the social presence enhancement strategies consistently showed more evidence of engaging in argumentation, especially higher level interactive argumentation, and in problem-solving processes; and (4) there is a significant difference in post-test problem-solving performance across conditions, where students in the condition that received both the question prompt scaffolds and the social presence enhancement strategies performed significantly better than students in the control condition. The study's findings underscore the importance of supporting students' social presence to engage them in interactive argumentation and problem-solving processes, thereby enhancing their problem-solving performance. This study contributes to the understanding of argumentation scaffolding and social interactions in asynchronous online discussion environments and provides design recommendations for instructional designers and instructors seeking to support students' argumentation and social presence in these environments. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]