This thesis explores the success of elementary school students in solving word problems in mathematics that involve different representations of numerical data, where the numbers are presented either as digits or as number words. The thesis is divided into theoretical and empirical parts. In the theoretical part, the fundamental principles of mathematics education in elementary school are elaborated, with a focus on the importance of understanding word problems. Various factors that may influence students' success in solving such problems are also analyzed, including cognitive development, language skills, and different methods of teaching mathematics. Special attention is given to the difference between tasks where numbers are presented as digits and those where they are presented as number words, and how this difference might affect the comprehension and solving of these problems. The empirical part of the thesis includes a study conducted among second, third, and fourth-grade elementary school students. The sample included 211 students from several elementary schools. The students solved a series of word problems in which the numbers were presented in two different ways. The aim of the study was to determine whether there is a difference in the success of solving problems depending on the representation of the numbers and to examine students' attitudes towards such tasks. The results of the research showed that, although there are minimal differences in success between tasks with numbers presented as digits and those presented as number words, third and fourth-grade students still demonstrate slightly better success in tasks where the numbers are presented as digits. The study also revealed that most students have a positive attitude towards solving word problems, which is an important aspect of their further motivation and success in mathematics. At the end of the thesis, recommendations are made for improving the methods of teaching mathematics in elementary schools, with the aim of increasing students' success in solving word problems, as well as guidelines for further research on this topic.