Understanding and evaluating an adolescent's struggles are rarely straightforward. Although mood,behavior, and common developmental challenges can appear similar on the surface, they are oftendriven by distinct underlying factors. User's Guide for the Structured Clinical Interview for the DSM-5 Alternative Model for Personality Disorders, Module I, Adolescent Version, helps clinicians go deeper by asking better questions, allowing for clearer, well-supported conclusions when administering and scoring the Module I-A interview for the Level of Personality Functioning Scale (LPFS) in adolescents. This guide outlines a semistructured interview process that focuses on understanding how adolescents function as people in their relationships—with themselves and others. By evaluating the four LPFS domains—Identity, Self-Direction, Empathy, and Intimacy—and applying clear scoring anchors, clinicians can translate observations into clear ratings that support treatment planning and collaboration with care teams. Designed for psychiatrists, psychologists, behavioral pediatricians, and other mental health professionals, this User's Guide is a practical, reliable companion to the Module I-A interview for assessing adolescent personality functioning.