Teaching and developing student competence is the central goal of the general education program. Students' reasoning skills play an important role in helping students have a foundation for thinking methods, ways of exploring and discovering. This is one of the factors that educates students to be capable of lifelong learning, educating new people to meet modern social requirements. In this article, we study students' reasoning skills and their expression. On that basis, we propose teaching measures to develop reasoning skills for 5th graders in teaching numerical content and calculations. As a result, there are 4 proposed measures and specific illustrative examples that contribute to improving the quality of teaching.