This research was conducted with the aim of determining the Influence of the Cooperative Learning Model of Group Investigation (GI) on student learning outcomes in mathematics for fourth-grade students at SDN 0306 Sosopan. The population in this study consisted of 48 students, divided into Class IV A with 24 students and Class IV B with 24 students. The research sample consisted of 24 students selected using the Total Sampling technique. The research type employed was an experiment with a Quasi-Experimental Design of the Pretest-Posttest Control Group Design. The research procedure included preparation, implementation, and conclusion stages. Before conducting the research, an instrument validation test, reliability test, difficulty level test, and discriminant power test were conducted. Subsequently, a pretest was administered to both classes, with the experimental class receiving treatment by implementing the Group Investigation (GI) learning model, while the control class used a conventional model. Finally, a posttest was administered to both classes. Data were analyzed using SPSS 24, including tests for normality, homogeneity, and hypothesis testing. Based on the students' learning outcomes, the experimental class obtained an average score of 41.04 in the pretest, which increased to 77.08 in the posttest. Based on the research results, it can be concluded that there is an influence of the Group Investigation (GI) learning model on student learning outcomes in mathematics for fourth-grade students at SDN 0306 Sosopan.