The purpose of this meta-analysis was to examine the effects of Gamified-Assessment Tools (GAT) used in formal educational settings on student academic achievement. We used PRISMA systematic procedures to screen the articles across Web of Science, ERIC, Scopus, Pubmed, and PsycArticles databases. We identified 23 independent results from 17 primary studies with academic achievement outcomes using GAT in formal educational settings. These primary studies accounted for a total of N = 2836 (n = 1318 in GAT, n = 1518 in control) participants. We evaluated publication bias and quality assurance of selected studies for the validity and reliability of our meta-analysis results. Publication bias was not determined as a threat to overall Effect Size (ES). We employed Random-Effects Models (REM) to calculate the overall effect size. According to the REM, the overall effect of the GAT on academic achievement was calculated as g = 0.62 at the medium level. We also examined the learner stage, learning domain, sync type of assessment tools, research design, and assessment tool as moderators in which GAT may be effective. ESs of GAT significantly differed according to the learner stage. GAT had a larger ES on academic achievement in higher education than K12. There were no significant differences in the ESs of the GAT for other moderators. Quizizz, which is the most effective assessment tool according to our results, has a large ES on academic achievement. Especially in K-12, more experimental research is needed to gain a deeper understanding of the effects of GAT.