In order to continue to improve the effectiveness of psychotherapy, researchers must identify key change processes. Unfortunately, there are disparate views in the field about the relative importance and potency of specific techniques versus relationship factors. Few measures have been developed to examine the relative contribution of these factors, particularly for child-focused treatment. The Common-Factor Therapist Competence Scale for Youth Psychotherapy (COMP-CF) was developed to address this deficit. For this study, 142 video-taped sessions of child CBT for anxiety were observed and rated by independent coders using the COMP-CF. The measure demonstrated good reliability and internal consistency. Significant between-therapist and between-session differences were noted that warrant further exploration. The COMP-CF also demonstrated initial validity when compared to other observer-rater measures of therapeutic processes such as alliance, CBT-specific competence, and adherence. Recommendations for further development and refinement are discussed. Used in conjunction with adherence measures, the competence measure developed here may help improve our understanding of the therapeutic process.