The study examined the influence of peer instruction on students’ achievement in tertiary education. The study was conducted in Ignatius Ajuru University of Education, Rivers State, Nigeria. The researchers adopted a non-randomized pretest-posttest control group design. The population of the study consists of 1,162 final year undergraduates, duly registered in a compulsory course: “Introduction to Special Education”. A sample of 486 students (200 males and 286 females) were drawn through proportionate stratified random sampling. Students in intact classes were assigned to the experimental and control groups. Students in the experimental group were exposed to lectures by the researchers and peer instruction, while those in the control group were only exposed to lectures by the researchers. The instrument for data collection was students' examination and continuous assessment scores, obtained after one semester of instruction. Three null hypotheses were drawn from three research questions postulated for the study. An analysis of covariance was used to analyze the data, which revealed a statistically significant difference between the achievement of experimental and control groups of students based on exposure to peer instruction.