In this study, it is aimed to examine the mathematical conceptual skills of 48-72-month-old children attending pre-school education institutions providing a Montessori Approach and Ministry of Education Pre-school Program (MoE PSP). The study group consisted of 20 children, who were trained by the Montessori Approach, and 20 children, who continued to attend pre-school education institutions applying the MoE PSP. The research was carried out in accordance with the state study design of the qualitative research methods, and the data of the study was collected by the structured observation method at the free play/individual work time in the learning centers of the children constituting the study group. A structured observation form was used as the data gathering tool, and mathematical concept skills such as counting, matching, grouping, comparison, positioning, measurement, pattern, part-whole, transactions and creating a graphic were included. Research data were analyzed with descriptive analysis method, and the frequency and percentage values of the obtained data were calculated. As a result of the study, it was observed that the students trained with the Montessori Approach and MoE PSP could not create graphics in both groups while the rhythmic counting and patterning skills were the most frequently observed skills in children. It has been determined that children are trained with the Montessori Approach complete more studies, especially on matching, grouping, comparison/ranking, and part-whole skills, compared to the children trained with MoE PSP. In the light of the results obtained in this research, it is suggested that the play materials that had to be in classes where MoE PSP was applied should be standardized, and children should be able to get through these materials; also mathematics center should be established in the class level.