With the increasingly ubiquitous nature of mobile devices among K-12 students, many argue for and against the inclusion of these devices in K-12 classrooms. Arguments in favor cite instant access to information and collaboration with others as positive affordances made possible through mobile devices. Self-directed learning, a process where individuals take charge of their learning and decide what they will learn, how they learn it, and how they assess their learning, has been identified as an increasingly important trait for K-12 students. The relationship between mobile device access in K-12 education settings and student self-directed learning has not been explored. This research used a mixed-method approach to learn more about the impacts of mobile devices on student achievement and self-directed learning during a Science, Technology, Engineering, & Mathematics (STEM) activity in a K-12 technology and engineering education classroom. In this study, 706 middle school students from 18 classes worked in groups of 2-3 to complete an open-ended engineering design challenge. Students completed design portfolios and constructed prototypes (products) in response to a provided engineering design challenge. Participating classes were divided with some receiving ubiquitous access to mobile devices during the study while others did not. Additionally, randomly assigned classes completed the design portfolio electronically while others completed their portfolios on paper. Final student portfolios and products were assessed and assigned a rank order using an innovative method of assessment called adaptive comparative judgment (ACJ). In ACJ judges view two artifacts (portfolios or products) electronically via a computer and choose the better of the two. Repeating this process, a number of times produced a rank-order for the artifacts. The rank order for student portfolios and products was used to represent student achievement. Statistical analyses of student access, portfolio type, student self-directed learning, and student achievement were conducted. In addition to the quantitative approach, 30 student interviews and 5 teacher interviews were conducted by the researcher following qualitative methodology. Interviewees were asked a variety of questions regarding mobile devices, self-directed learning, open-ended engineering design challenges, and their experience during the study. Responses from the interviews were transcribed and coded using causation and thematic coding techniques. The resulting themes from the interviews were compared with the quantitative findings. Findings from both the quantitative and qualitative analyses showed that student access to mobile devices was significantly correlated with higher scores on student design portfolios while student achievement on design products was independent of mobile device access. These findings suggest that mobile devices may improve student achievement in certain types of scenarios but not in others. Over the course of the study, student self-directed learning was independent of mobile device access. Students and teachers both commented that mobile devices may be effective at increasing student self-directed learning or achievement but only through proper instruction and demonstrations. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]