This meta-analytic study focused on the quantitative integration and synthesis of the accumulated pedagogical research in undergraduate statistics education literature. These accumulated research studies compared the academic achievement of students who had been instructed using one of the various forms of small-group learning methods to those who had been instructed using lecture-based instruction. The meta-analytic results showed that cooperative, collaborative, and inquiry-based learning methods were used in college-level statistics courses. The results also showed that cooperative and collaborative learning methods supported the effectiveness of the small-group learning methods in improving students' academic achievement with an overall average effect-size of 0.60. In contrast, the effectiveness of inquiry-based learning was close to zero. This significant positive average effect-size indicated that using small-group learning methods in statistics classrooms could increase the achievement of college students, increasing the scores on a statistics exam from the 50th to the 73rd percentile. In addition, the multilevel analysis revealed that the effect sizes were influenced significantly by the publication-year of the studies, with the most recently published studies having lower effect sizes. The major implication of this study is that evidence-based research supports the effectiveness of active small-group learning methods in promoting students' achievement in statistics.