Gamification is widely used to enhance student learning and engagement. This meta-analysis focused on experimental research examining the effects of gamification on student motivation in K-12. Studies were retrieved from Scopus, PubMed, Web of Science, and ProQuest, resulting in 279 articles screened, with 31 meeting the inclusion criteria. The pooled effect size (k = 41) for gamification was g = 0.654 (95% CI [0.442, 0.866]) under a random effects model, with high heterogeneity observed (I2 = 88.92). Unlike previous meta-analyses, this study simultaneously compared gamification's effects on intrinsic versus extrinsic motivation and analyzed grade-level differences across primary, secondary, and high school students. Gamification had a greater impact on extrinsic motivation (g = 0.713, 95% CI [0.152, 1.275]) than intrinsic motivation (g = 0.638, 95% CI [0.239, 1.036]). Additionally, gamification was the most effective among secondary school students (g = 1.015, 95% CI [0.639, 1.391]), followed by high school students (g = 0.821, 95% CI [0.523, 1.119]) and primary school students (g = 0.309, 95% CI [0.033, 0.584]). These findings provide developmentally tailored, practical insights for designing effective gamified learning environments.