The paper presents the international research study conducted in selected Czech and Russian primary schools in 2020. This research was mainly focused on the issue of pupils' relationships with their classmates with special educational needs, who are inclusively educated in regular school classrooms. According to the research results, the attitudes of pupils towards their classmates with special educational needs are rather neutral or even slightly negative in primary schools in both countries. However, most teachers do not consider this a problem affecting the classroom climate at all, and it seems that they do not work effectively with this issue as they are not skilled in this area and do not master the appropriate techniques used in support of pupils' relationships and a quality classroom climate. Although there are some differences between the results in Czech and Russian primary schools, we can suggest the improvement in working with diversity, as well as the development of teachers' skills for teaching heterogeneous peer group in a school classroom.