The main purpose of this study was to determine the effectiveness of cooperative learning and peer-teaching strategies on students’ achievement and interest in Mathematics in Ezeagu Local Government Area of Enugu State. In addition, the study determined which of the two teaching strategies would be more efficacious in enhancing students’ achievement and interest in Mathematics. Six research questions and six hypotheses were formulated to guide the study. The research work was quasi-experimental design type, specifically the non equivalent control group design. Two hundred and eighty three Mathematics students drawn from nine co-educational public schools within the Ezeagu Education Zone of Enugu State were used for the work. Simple random sampling technique was applied in choosing the schools as well as assigning each of the teaching approaches to the sample schools. The cooperative learning and peer –teaching groups were the experimental groups while the conventional teaching method group was treated as the control group. Validated Mathematics Achievement Test (MAT) and Mathematics Interest Inventory (MII) were administered to the students as pretest and posttest for collection of data. The MAT had reliability index of 0.98 while MII had reliability index of 0.93. The mean scores were used to answer the research questions while analysis of covariance (ANCOVA) was used to test the hypotheses at 0.05 level of significance. From the findings of the research work, teaching approach used in difficult mathematics concepts is significantly responsible for the perennial poor performance of students in secondary school mathematics and more of cooperative learning should be used as it has better effect on students interest and achievement in learning difficult mathematics concept than the peer teaching, a number of implications were discussed. Recommendations and suggestions for further studies were also made.