Preparing students for science, technology, engineering, and mathematics (STEM) education is one of the United States' K-12 educational concerns (Gandhi et al., 2016). Despite the National Science Foundation's (NSF) report that the number of students participating in STEM fields continues to increase, the number of underrepresented students entering the same programs continues to fall behind. Research shows that students' success in STEM education is highly correlated with their spatial visualization skills (Park, Kim, & Sohn, 2011; Katsioloudis et al., 2016). One of the ways to increase underrepresented students' participation in STEM-related fields is to focus on students' self-efficacy. The present study examines how learning 3D design modeling impacts students' STEM self-efficacy and career decision-making. In particular, this study investigated the impact of an 8-week asynchronous learning program for underrepresented senior high school students who live in rural North Carolina. During the 3D modeling course, students learned how to use OnShape computer design software online to create their own designs to 3D print them. The result showed that having a real-world experience through a 3D modeling along with mentorship had a positive impact on high school students' STEM self-efficacy and their interest in STEM fields. [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.]