In the presented contribution, we address the issue of forming a mutual relationship and establishing cooperation between the teacher and parents. At the beginning of schooling, the establishment of high-quality cooperation between the teacher and the pupil's parents is an important aspect of supporting the successful school adaptation, academic results and comprehensive personality development. In the contribution, we also pay attention to the formation of the cooperation competence of the teacher in undergraduate training and in the framework of his professional development. The aim of the contribution is to carry out a theoretical analysis of the selected issue and, in particular, to find out the prerequisites for cooperation and the determinants of the mutual relationship between teacher and parent. For this purpose, we carried out pedagogical research in practice. By conducting research and analyzing research findings, we found that teachers consider gaining parents' trust to be the most important prerequisite for cooperation with parents. According to the results, the mutual relationship between the teacher and the parents of beginning pupils is most influenced by the willingness to communicate with each other, and the type of parent is also a significant determinant.