The propagation of augmented reality (AR) and virtual reality (VR) applications that leverage smartphone technology has increased along with the ubiquity of smartphone adoption. Although AR and VR technologies have been widely utilized in the educational domain, there remains a dearth of empirical research examining the differences in educational impact across AR and VR technologies. The purpose of our exploratory study was to address this gap in the literature by comparing AR and VR technologies with regard to their impact on learning outcomes, such as retention of science information. Specifically, we use a two-condition (AR vs. VR) between-subjects' design to test college students' science-knowledge retention in response to both auditory and visual information presented on a Samsung S4 smartphone app. Our results (N = 109) suggest that VR is more immersive and engaging through the mechanism of spatial presence. However, AR seems to be a more effective medium for conveying auditory information through the pathway of spatial presence, possibly because of increased cognitive demands associated with immersive experiences. Thus, an important implication for design is that educational content should be integrated into visual modalities when the experience will be consumed in VR, but into auditory modalities when it will be consumed in AR.