Strengthening social and emotional skills can be particularly relevant concerning the emerging skills need as it yields benefits for individuals’ successful development. A growing body of research suggests that social and emotional competences are associated with well-being and positive life and academic outcomes. Despite the notable benefits of social and emotional skills, assessment tools are still scarce or target specific risk and problematic behaviours. This systematic review seeks to address this gap and identify instruments measuring social and emotional skills for students in elementary through secondary education. This review also aims to describe the study characteristics and key features of the identified instruments and to assess the extent to which the instruments comprehensively evaluate the five Collaborative for Academic, Social, and Emotional Learning (CASEL) areas of competence. A systematic search of the literature was carried out in Scopus, Web of Science and ERIC databases. This review resulted in the identification of 25 unique assessments over a 20-year period, reported on the basis of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Our results suggest a rapid growth and notable advancements of social and emotional skills assessment systems and demonstrate the direct influence of the CASEL framework. Our results also show that a combination of multi-method and multi-informant assessment should be employed to effectively assess social and emotional skills. Thus, this paper contributes to support school-based practitioners and psychologists in their efforts to lead social and emotional skills instruction and assessment in routine educational practice.