The assessment of psychosocial strengths in children and adolescents has predominately focused on the measurement of single traits and constructs, such as grit (Christopoulou, Lakioti, Pezirkianidis, Karakasidou, & Stalikas, 2018), optimism (Oberle, Guhn, Gadermann, Thomson, & Schonert-Reichl, 2018), hope (Pedrotti, 2018), and gratitude (Gottlieb & Froh, 2019). Although there is substantial value in assessing and evaluating the beneficial correlates of individual constructs, we suggest that a whole-child paradigm (Alford & White, 2015) provides an optimal rationale supporting the use of comprehensive measures of psychosocial strengths. Strength-based measures have a clinical purpose when used by school psychologists as part of an individual child psycho-educational assessment, but we suggest that such measures have even greater utility when used to provide comprehensive information about psychosocial strengths of "all" students within the ecological context of local education agencies. In our chapter, we focus on strength-based tools developed for schoolwide universal screening. A second consideration that guides this chapter is that psychosocial strengths-based assessment has critical benefit and scientific rationale when grounded in a sound conceptual model that offers an understanding of the process and factors associated with quality of life outcomes among adolescents. [This will be a chapter in: "Handbook of Positive Psychology Assessment: Psychological Assessment -- Science and Practice." European Association of Psychological Assessment (EAPA). Preparation of this chapter was supported in part by a research grant from by the Spanish Ministry of Economy and Competitiveness.]