This analysis provides the first known in-depth qualitative inquiry into if and how juvenile court judges take the psycho-social immaturity and development of adolescents into consideration when making attributions of adjudicative competency of offenders in juvenile court. Semi-structured interviews were conducted with twenty-seven U.S. juvenile court judges, followed by grounded theory analysis. Competency evaluations from psychologists and the juvenile’s age, history, awareness, and mental capacity influence judicial determinations of competency. Although data show that understandings of adolescent development do play a large role in shaping judges’ understandings of juvenile behavior—particularly related to emotional control, irrational behavior, lack of maturity, and social susceptibility—most judges only connected these characteristics to juvenile offending. Although cognizant that juveniles exhibit attributes that diminish competency-related abilities as part of their adolescent development, the majority of judges still stated that adolescent development is not important to them in assessing juvenile competency, potentially demonstrating a cognitive disconnect on these issues. These results indicate approaches to how judges might think about juvenile competency decisions (“building blocks” vs. “holistic” models) and the need for more direct education and training of judges on the role of adolescent development in competency.