Implications of different methods for specifying classroom composition of externalizing behavior and its relationship to social-emotional outcomes.

•We examine implications of methods for using individual data to represent classrooms.•Chicago School Readiness Project data are used to model classroom effects.•The mean is not often predictive of classroom composition for later outcomes.•Children in classrooms with homogeneous behaviors have better kindergarten outcomes.•A child's value in relationship to the class mean is salient for later outcomes.