Positive judgments on the Self are good predictors of academic achievement. It could be useful to benefit from an instrument able to assess how pupils elaborate self-judgments. So far, such a tool does not exist. The purpose of the present study was to develop a self-report measure of social judgment for children at school (the School Social Judgment Scale--SSJS). 660 pupils completed a questionnaire addressing 12 socio-academic behaviors. An exploratory factor analysis highlighted a four-factor structure of social judgment (Assertiveness, Competence, Effort and Agreeability). A Confirmatory Factor Analysis (CFA) provided further support for this model, both in terms of factorial and construct validity. Reliability ranged from questionable to good depending on SSJS subscales. Multigroup CFA revealed invariance of the SSJS across gender and showed that boys had higher scores than girls for the assertiveness scale. Overall, the SSJS represents an efficient tool to better understand how social judgment for children works. As such, it could assist professionals of education to develop suitable educational support to assist poorly performing children at school.