This study aims to assess the impact of mobile augmented reality (AR) applications on the astronomy competencies of middle school students in Vietnam, addressing the gap in practical educational mobile applications within science, technology, engineering, and mathematics (STEM) fields. Employing a quasi-experimental design, the study involved 438 sixth graders from four middle schools in Central Vietnam over eight weeks. The experimental group utilized AR applications, while the control group received conventional textbook instruction. Astronomy competencies were evaluated through pre-and post-tests, employing self-developed questionnaires based on standardized assessments. The results indicated that students in the AR group outperformed their counterparts in the control group across key competencies, including celestial motion, spatial orientation, and conceptual understanding. Notably, analysis of spatial learning revealed that female students in the AR group performed better than their male peers. Interviews with participating students suggested that AR applications enhanced interactions and facilitated a better understanding of abstract concepts, although some technical issues were reported. These findings highlight the potential of mobile AR to improve short-term learning outcomes and suggest its role in narrowing gender gaps in STEM education. Future research should investigate the long-term effects of AR on learners and explore its application across diverse learning environments while considering infrastructural and socio-cultural constraints. © 2024 by the authors of this article.