We examined differences between school classes with respect to three aspects of psychosocial adjustment at school, namely the extent that children in the class liked to play with each other, the number of teacher-reported behaviour problems, and children's feelings of well-being at school. The sample consisted of 1282 4- to 5-year-olds from 94 school classes and 51 schools, but due to nonresponse actual sample sizes were somewhat smaller for most analyses. Multilevel analyses showed that on average 87% of the variance was at the child level, 11% at the class level, and 3% at the school level. This indicated that a non-negligible amount of variance could not be accounted for by factors at the child level. Furthermore, this variance was mainly associated with differences between classes instead of differences between schools. A set of variables that pertained to sociodemographic characteristics of schools, school facilities, organisational aspects of classrooms, and the teacher did not provide an adequate explanation for the differences in adjustment levels. In contrast to these traditional variables, social network indices yielded substantial correlations, showed consistent trends across the different adjustment measures, and fulfilled the necessary requirement that to explain differences between school classes the predictor variables themselves should differ for classes within the same school. These results suggested that aspects of the interpersonal relations of children in the classroom such as proximity, integration, and the amount of contact could be determinants of differences between school classes in psychosocial adjustment.

Within the “Wrocław Longitudinal Twin Study” in a part of the material the liking level of singletons (SIN) to identical twins (TMZ) and of TMZ to SIN was analysed cross-sectionally, in the period of 11th to 18th year of life. In each of the 76 classes of elementary and high schools in Wrocław (Poland), including the investigated in 1976-7 TMZ (64 pairs), were evaluated the relations between school-mates, using the Korczak's five-degree scale of liking. The declared by TMZ and SIN liking decreased with age between pupils of the same sex, and increased between pupils of opposite sex, however, in TMZ with some delay. The liking declared by TMZ of both sexes to SIN was on average lower than that declared by SIN to TMZ. The degree of liking declared by SIN to TMZ of the same sex was average higher than in relation of SIN to SIN particularly among girls. Thus, there occurred the so-called “prima donna effect”. The liking declared to pupils of opposite sex in relation of SIN to TMZ was on average lower than the analogous one in relation of SIN to SIN and in relation TMZ to SIN even worse. The higher contrast in treating pupils of the same and opposite sex in TMZ than in SIN indicates a lower social maturity in TMZ. A diverse influence of socio-economic conditions on the declared toward then liking by boys and girls was found. The low number of separated twins did not allow to make a generalisation on specificity of their position in class. The sending of TMZ to different classes appeared to be in Wrocław elementary schools sporadic (1 repeater), and in high schools observed in 38%, from that 28% of twins went to equivalent classes, usually in different school, and in 10% of pairs one of the twins repeated the class.

A representative sample of 55 mainstreamed 9–10-year-olds with hemiplegia were compared with all classmates on sociometric measures of popularity and friendship, and with 55 matched controls on measures of victimisation. Children with hemiplegia were more rejected and less popular, had fewer friends, and were more often victimised; they were not more likely to be bullies themselves. These differences were not fully accounted for by group differences in teacher-estimated IQ and behaviour. Possible explanations range from neurologically determined deficits in mentalising skills to peer prejudices about children with disabilities. The development of appropriate intervention strategies should be a high priority, particularly since peer problems not only result in current distress but also predict psychosocial problems in the future.