This manuscript describes the development and psychometric testing of an instrument to assess implementation fidelity of Together Facing the Challenge (TFTC), an evidence-based approach to treatment foster care (TFC). The development of TFTC utilized a hybrid approach by bringing together components from evidence-based interventions with data on “what works” in usual care treatment foster care to create an intervention designed to provide enhanced treatment across a wide range of treatment foster care programs. The resulting training/consultation model has shown positive results on practice and youth outcomes in a randomized trial. The TFTC-FIT was developed during this randomized trial to be used as both a research measure and a quality improvement tool by provider agencies. Findings show that the measure is psychometrically sound and significantly distinguishes agencies trained in TFTC from those that are not. Discussion highlights the potential for such a measure, both in treatment foster care and in other home-/community-based interventions and settings for youth.