Consultation is an important implementation strategy to improve treatment fidelity and clinical outcomes, yet research has not identified the aspects of consultation that differentially affects clinician skill development and client symptom change. Thus, the present study investigated the effect of the consultant, consultation activities, and consultants' (n = 6) perceptions of consultees (n = 60) on post-traumatic stress disorder (PTSD) treatment fidelity and client outcomes. In addition, we assessed the accuracy of consultants' evaluations of clinicians using the Perceived Enthusiasm, Skill, and Participation scale (P-ESP). Results indicated that there was a significant effect of consultant on adherence to, but not competence in, delivering Cognitive Processing Therapy (CPT). The effect of the consultant on PTSD symptom change was not significant. Consultants significantly differed in their discussion of CPT strategies and their application to individual cases, but did not differ on reviewing and providing feedback on fidelity. Consultant perceptions as assessed by the P-ESP were not associated with clinicians' current levels of adherence or competence, suggesting that consultants may not accurately assess clinician skill during consultation. Client PTSD symptom change neither predicted, nor was predicted by, consultants' perceptions of their consultees' skill. This article outlines potential reasons for consultant effects and possible biases at play that may reduce the accuracy of consultant perceptions and presents suggestions on alternative strategies to assess clinician skill during consultation. (PsycInfo Database Record (c) 2022 APA, all rights reserved).