This work presents the result of some reflections on the teaching of mathematics, especially in the areas of arithmetic and algebra, addressing contents related to the numerical sets present in the mathematics curriculum of elementary school II. The objectives of these reflections were to verify how important the semiotic records can be (see chapter 4, section 4.2.1), the zone of proximal development theory (ZPD) derived from the socio-constructivist theory (see chapter 4, sections 4.2.2 and 4.2.2.1), and the use of the calculator in the investigation of decimal numbers and in the study of numerical sets. Based on a democratic space that values dialogue, the student s daily life with the world of mathematics and using the exchange of experiences between them, we aim to understand concepts and meaningful learning about the contents covered. Arithmetic, in particular, requires a careful look at the representations and operative properties that a number can present. The development of methods that stimulate this view makes the student s understanding of decimal numbers gain important and considerable meanings. Finally, this work also defends the question of the use of technology in school through the oriented use of calculators, in mathematics classes, as a pedagogical resource that can prove to be quite efficient, since technology is increasingly present in the daily life of society. The results of these reflections were translated into the development of an applied activity with the students, and were exposed throughout this work. This activity was applied predominantly in classes of the seventh year of elementary school, since they have the necessary prerequisites for the questions proposed in it, but they have not yet had great contact with the content proposed by this activity. It was also applied to an eighth grade class, as a parallel recovery activity. We have also created an interesting activity for addressing irrational numbers in which we explore right triangles. We hope that these reflections can collaborate in some way in basic education, for the development of a more autonomous and meaningful mathematics education.