A cohort longitudinal design with four adjacent cohorts of students (n= 1689) followed over two years was used to study key issues identified in the research literature on the development of self‐evaluations in early adolescence. There was no clear relationship between age/grade and self‐evaluations. We found no support for a “stressful periods” hypothesis with respect to self: Possible changes were very gradual and quite small. However, there was a consistent “relative age” effect implying that younger students within a grade had more negative self‐evaluations. There were small but consistent sex differences in self‐evaluations in favor of the boys; more detailed analyses of very negative self‐evaluations suggested that the early adolescent years are the period in which a sex difference in depression related symptomatology begins to emerge. Finally, the usefulness of some kind of effect size measure and advantages and problems associated with a cohort longitudinal desi