Social Studies as a school subject plays a pivotal role in developing students’ civic competence, critical thinking, and understanding of societal values. However, persistent challenges such as poor academic performance, low retention of concepts, and limited engagement among students have raised concerns about the effectiveness of conventional teaching methods. This study examined the effect of Cooperative Learning Strategy (CLS) on students’ academic performance and retention in Social Studies among Junior Secondary School (JSS II) students in Ekiti State, Nigeria. The study adopted a quasi-experimental research design using a non-randomized pretest-posttest control group. The population comprised all JSS II Social Studies students in Ekiti State, from which 115 students were selected through purposive sampling for schools and intact class sampling for students. The experimental group was taught using the Cooperative Learning Strategy, while the control group received instruction through the conventional lecture method. Two instruments were used for data collection: the Social Studies Achievement Test (SSAT) to measure academic performance and the Retention Test (RT) to assess knowledge retention. The instruments were validated by experts in Social Studies education and educational measurement, and their reliability was established through KR-20 and test–retest methods with coefficients of 0.86 and 0.82 respectively. Data collection followed a structured process involving a pretest, intervention, posttest, and a delayed retention test four weeks later. Data were analyzed using mean, standard deviation, and Analysis of Covariance (ANCOVA) at a 0.05 level of significance. Findings revealed that students taught using CLS performed significantly better than those taught through the conventional method. The study also found that CLS enhanced students’ retention of Social Studies concepts, while gender did not significantly influence performance or retention. Therefore, it is recommended that Social Studies teachers adopt CLS to encourage collaboration, critical thinking, and sustained learning. Teacher training programs should also incorporate cooperative learning techniques to enhance pedagogical competence and student outcomes.