Children's school readiness implies their ability to adjust to the requirements imposed by school, to meet the teachers' criteria, to show progress in learning and to their abilities in general. The purpose of this research is to identify the critical incidents relating to children's school readiness. In the context of children's entry into obligatory primary education, there are numerous issues of key importance for a harmonious transition from the kindergarten environment to primary school. The data were collected during group discussions between kindergarten teachers (n = 12) and primary education teachers (n = 12), who were divided into four focus groups. The qualitative content analysis was performed, and the critical incidents were classified into four categories. Furthermore, focus groups were used as a method of designing questionnaires to examine the expectations of parents, kindergarten teachers and primary education teachers regarding children's readiness for primary school.