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 wellbeing 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.