This work aims to deal with the use of Peer Instruction as a methodology for Teaching Mathematics in Elementary School. Considering as a problem the difficulty in teaching and learning this discipline, this work seeks for developing the ability of students learning how to learn using Peer Instruction. The main objective of the work is to investigate Peer Instruction in the teaching of mathematics with fifth year students of Elementary School as an alternative in the construction of mathematical knowledge. The method consists mainly of the interaction between the students in order to promote the understanding of mathematical concepts compatible with their age group. The methodology adopted in the study was basically made up with questionnaires, which enabled students to learn about the traditional teaching of Mathematics, and tests that allowed students to evaluate their knowledge through prior reading, as well as acquired learning after interaction with other students during classes. Although not reaching all the students, the quantitative results, which deal with previous readings, show that this activity has a positive impact on the performance of the students. Concerning the results during interaction in the classroom, they demonstrated that students assimilate concepts more easily, as well as being able to participate actively in the classes, including helping other students with greater difficulties in learning the contents. The application of the Peer Instruction demonstrated that students feel confident, once they perceive their ability in how to learn, and more motivated, because the dynamics imposed by the active methodology adopted during the classes rises their interest in learning Mathematics and, as a consequence, students participate more effectively during classes. The results obtained in this work suggest that the Peer Instruction can be successfully applied in the Elementary School.