The goal of the current study was to develop and test a rigorous measure of therapist adherence to a cognitive-behavioral, manual-based treatment for childhood and adolescent depression. This project employed data from the recently completed UCLAYouth Anxiety and Depression Treatment study. This study aimed to advance the literature by devoting the full focus of the project to the development of a manual-based measure that would demonstrate interrater reliability across multiple raters. This study reported on the psychometric development of the PASCET Manual Adherence Scale (PMAS) (e.g. scoring strategy, item development, reliability), a unique measure of therapist adherence that represents the content of the treatment manual for the "Primary and Secondary Control Enhancement Training" program (PASCET; Weisz et al., 1999). In sum, the P-MAS showed strong interrater reliability for most items of the scale. The items with poorer ICCs may have been influenced by instrumentation problems, small sample size, and range restriction. Some session content showed evidence that more meetings may be required to sufficiently cover the material, particularly for those that involve heavy in-vivo content, require the use of technology, or involve cognitive interventions which may be challenging for children and young teenagers. The results indicated that therapists adhered to slightly more than half of the prescribed manual content overall. The variability in adherence appeared greater for session-specific content than for standard session items, reflecting the variability within that content and the myriad of factors which may have influenced adherence to diverse material. Adherence for session-specific content demonstrated a slightly downward trend over time, with a significant drop off between the first and second phases of treatment and a leveling off between second and third phases. For all but two relevant sessions, therapist adherence to didactic content was significantly higher than adherence to in-vivo content, highlighting the challenges of engaging depressed youth in active learning. As this active involvement is theorized to be an essential component in addressing depressive symptoms, the challenges in implementation of this content may represent the most significant barrier to therapist adherence with this manual.