This study titled “Evaluating the Effects of Class-Size on Social Studies Students? Academic Performance in Junior Secondary Schools in Giwa Educational Zone Kaduna State, Nigeria”. Three objectives, three research questions and three hypotheses each were formulated for the study. The study used quasi experimental design. The total population of public Junior Secondary Schools students in Giwa Educational Zone was 5449 from which a sample of three hundred and eighty three (383) students were selected using random sample technique. Furthermore, four (4) schools were purposely selected. The study used pre-test and post-test group design. The students were further grouped into two groups (i.e. Group A: large class-size and Group B: small class-size). The main instruments used for the data collection was Social Studies Students Academic Performance Test (SOSSAPET). The pilot study has the reliability coefficient of 0.551. T-test statistic was used to test the null hypotheses at p<.05 level of significant. The study revealed that students mean scores performance was higher in small class size than large class size. There was no significant difference in the mean academic performance scores of male and female students when the class size and sex were considered together. There was no significant effect on students performance based on the school location in small class size and those in large class sizes. Based on the results of the findings, it is recommended that small class size in teaching enhance students learning ability in Junior Secondary Schools. Government should decongest large classes by constructing more classes and upstairs in urban and rural areas so as to encourage students by allowing them to seat 40 or less than that quantity for effective teaching and learning. This will also promote students academic performance in Junior Secondary Schools.