Four decades of research have shown that students' low test-taking effort is a serious threat to the validity of score-based inferences from low-stakes, group-based educational assessments. This meta-analysis sought to identify effective interventions for improving students' test-taking effort in such contexts. Included studies: (1) used a treatment-control group design; (2) administered a low-stakes group-based educational assessment; (3) employed an intervention to improve test-taking motivation; and (4) evaluated test-taking effort and/or test performance as outcomes. The analysis included 53 studies (N = 59,096) that produced 60 and 105 effect sizes of test-taking effort and test performance, respectively. On average, interventions were found to improve test-taking effort and test performance by 0.13 standard deviations (SD) each. The largest gains in test-taking effort were observed when providing external incentives followed by increasing test relevance, while no significant differences were found between these two intervention types in improving test performance. Furthermore, negligible impact was detected on both dependent variables for interventions that modified assessment design or promised feedback. Recommendations for future research and practice are discussed.