This diploma thesis presents the educational reform from 1972 with an emphasis on teaching mathematics in the lower grades of elementary school. At the very beginning, the social and economic reasons that led to the initiation of changes in the educational system, are briefly described. Also, the New Math reform, that took place in 1960s has been presented and briefly described. With the New Math movement, new contents and methods are introduced into the teaching of mathematics, in order to enrich its curriculum and to keep pace with technological progress. Furthermore, the socio-economic conditions in the Socialist Republic of Croatia are presented. Those conditions led to the modification and improvement of the plan and program from 1958 and the creation of a new plan and program in 1972. The changes that the new plan and program brought up to the teaching of mathematics in the lower grades of elementary school are described and explained. Furthermore, the new plan and program’s determinants are listed, the goal and tasks are defined and the layout of the material and the way of working in class are shown. The changes derived by the new plan and program were highlighted, and math problems from textbooks were compared and analyzed. At the very end, the plan and program from 1972 was compared with today's curriculum. Also, task examples from textbooks and other teaching materials from 1972 were analyzed and compared with today’s materials. The aim of this thesis is to explain why and how the changes in the mathematic curriculum occurred in the first place there were changes in the mathematics curriculum and how the impact of those changes is represented in today’s teaching of mathematics.