The study examined the influence of class size on the teaching of mathematics in selected junior secondary schools within Akure North Local Government Area. Employing a descriptive survey design, the sample comprised 35 mathematics teachers drawn from seven schools. Data were collected using the Teachers' Classroom Size Questionnaire and analyzed through frequency counts, percentages, and mean scores. Findings indicated that most teachers agreed that large or overcrowded classes negatively impact the effective teaching of mathematics. The cluster mean score of 4.20, which was higher than thebenchmark mean of 3.50, confirmed that teachers perceived large class sizes as a major hindrance to instructional efficiency. In addition, teachers identified several factors contributing to the prevalence of large classes, with a cluster mean of 4.15, also above the criterion mean, suggesting broad consensus on the issue. The study therefore recommended that the government should provide additional classrooms and teaching facilities to reduce overcrowding and enhance instructional effectiveness in mathematics.