Augmented Reality (AR) has been continuously adopted in K-12 settings, showing its beneficial impact. Despite numerous studies highlighting the benefit of AR that can enhance students' motivation, no meta-analysis providing an in-depth look into AR's impact on students' motivation has been conducted, particularly in K-12 settings. In this meta-analysis, we meta-analyzed 45 experimental studies using AR in K-12 settings from 2010 to 2022, guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analysis procedure. We also conducted a moderator analysis considering diverse instructional considerations and study features, to offer a more focused and comprehensive understanding of AR's effect on K-12 students' motivation. The results showed a large effect of AR on enhancing K-12 students' motivation (g = 0.803). Furthermore, we found that marker-based AR and collaborative learning significantly promoted K-12 students' motivation, compared to location-based AR and non-collaborative learning experiences. The results indicated AR in K-12 settings needs to be carefully designed, considering how it is integrated within pedagogical practice. The implications and future research direction for researchers, educational practitioners, and AR developers are also discussed.