Montessori pedagogy rests on the basic principles that Maria Montessori has set up with scientific observation of children and their behavior. The purpose of this paper is to explore and theoretically confirm the basic principles of Montessori pedagogy and to describe how the Montessori Primary School "Barunice Dédée Vranyczany" in Zagreb applys these principles. The emphasis was on the following principles: the specially prepared environment in which the research was conducted, the behavior of the pupils, the specialty of social learning when mixing ages, the role and incremental assistance of Montessori teachers and freedom and the discipline about what spoke Maria Montessori. The research was conducted with observation without participation and the notes were kept during each observation in the previously designed observation form. There were six observations over the period of three months. Students of grades one to four (N = 63) and their teachers (N = 8) were observed. The results of this research are the notes created during the observation, and it has been established that in the school practice of the Montessori Elementary School "Barunice Dédée Vranyczany" there is consistency in the application of all observed principles of Montessori pedagogy and the expected behavior of the pupils are noticed by the Montessori pedagogy principle.