The Integrated System of Differentiated Assessment for Adolescents and Youths, (SIED-AJ for its Spanish Acronym) is a diagnostic instrument aimed at recognizing the offending adolescent and/ or youth, as subject of Law who is at a specific development stage and where their resources, potentialities and risk factors (or vulnerability) may be recognized in order to identify levels of complexity and thus advise on differentiated, specific and focused interventions in accordance with their needs.The SIED-AJ is a practical, theory-and evidence-informed tool; it consists of 8 variables with their applicable dimensions and categories aimed at generating a type of retrospective analysis also exposing elements which define the intervention process management with specific criteria for each variable in order to modify the occurrence of crime-typed behaviours.