A dual approach to mental health in schools has been widely defended, where the assessment of psychological distress and the examination of strengths/well-being are two separate continua. In line with a well-being approach, school belonging has been referenced as an important indicator of mental health in children. This study explored the predictive role of school sense of belonging alongside other demographic variables (gender, main language spoken at home, and socio-economic status of postcode) on the socio-emotional health profiles of primary school children in England. Children (N = 522) were recruited from three primary schools in Greater London. A survey including measures of school belonging and socio-emotional health was administered to all children. Results showed that it is possible to identify groups of students at primary school level based on "socio-emotional health ratings on gratitude, zest, optimism, and perseverance." School sense of membership, as measured by the psychological sense of school membership primary (PSSM-P), was the best predictor of group membership and, together with socio-economic status, explains 37% of the variance in socio-emotional health profiles. Belonging starts affecting well-being and socio-emotional health as early as in primary school, hence the importance of universal screening and early preventive actions to promote well-being in this age range. The study provides evidence supporting the use of the abbreviated (PSSM-P) in predicting socio-emotional health profiles, with potential to complement distress-based measures.