This dissertation, utilizing a mixed-methods approach within a design-based research (DBR) framework, investigated the impact of augmented reality (AR) technology on the self-efficacy of preservice elementary teachers (PSTs) in integrated STEM teaching and technology. Incorporating both a pilot study and a subsequent dissertation study, the research specifically focused on the effects of AR GeoGebra. The key results that emerged from the pilot and dissertation studies highlight AR's potential to significantly enhance PSTs' STEM teaching self-efficacy. In both studies, the treatment group that engaged with AR GeoGebra showed substantial improvements in integrated STEM teaching self-efficacy. Additionally, in both studies, participants from all groups exhibited significantly improved technological self-efficacy after using GeoGebra, regardless of AR exposure. Qualitative data underscored AR's role in promoting hands-on learning, fostering creativity in STEM education, and bolstering positive attitudes towards STEM integration. These findings emphasize the transformative potential of AR in STEM teacher preparation and its capability to address the needs of preservice teachers in technology-enhanced educational 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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]