<![CDATA[Background: In response to the growing need for student-centered learning approaches in elementary education, the Group Investigation (GI) model offers a collaborative framework that encourages active participation, critical thinking, and meaningful learning. Thematic learning, which integrates multiple subjects around a central theme, benefits from such interactive models that foster deeper understanding and engagement. Objective: This study examines the impact of the Group Investigation (GI) learning model on students' learning outcomes in thematic learning at SD IT UMMI Kota Bengkulu. Method: Using a quantitative experimental approach with a nonequivalent group posttest design, this research compares students' learning outcomes between an experimental class (applying the GI model) and a control class (using conventional methods) through pretests and posttests. Results: The GI model had a significant effect on students' learning outcomes. The mean score of the experimental class (0.46) was higher than that of the control class (0.35), with a confidence interval of the difference ranging from 0.10 to 18.77 at a 5% significance level. This indicates an average learning outcome improvement of 0.10. Conclusion: The GI model is effective in enhancing conceptual understanding, social interaction, collaboration, and critical thinking skills among students. Originality/Value: This study offers novel empirical insights in the field of elementary education by demonstrating the significant effectiveness of the Group Investigation (GI) model in improving students' thematic learning outcomes (experimental mean of 0.46 vs. control mean of 0.35) while simultaneously fostering critical thinking, collaboration, and conceptual understanding within the context of integrated thematic learning in primary schools, an area with limited empirical examination. These findings enrich the body of empirical evidence and serve as a strategic reference for implementing student-centered, collaborative instructional strategies and advancing elementary curriculum delivery methods.]]>
