Identifying core elements of family therapy is a relatively new line of research that has the potential to increase the availability of family therapy in usual care by proving a flexible and accessible alternative to manualized treatment. The current study extends this line of research by exploring the psychometric properties of a Caregiver Engagement factor comprised of four caregiver engagement interventions grounded in family therapy theory and clinical expertise: Enhances Love and Commitment, Caregiver Collaboration, Caregiver Ecosystem, and Joins with Caregivers. The study sampled a total of 320 audio or video recorded sessions and outcome data from 152 cases treated by 45 therapists participating in one of three randomized trials investigating delivery of family therapy for adolescent behavior problems in community settings. Construct and predictive validity were analyzed to understand the degree to which caregiver engagement items cohered as a single factor and influenced youth and family outcomes in predictable ways. Results demonstrated reliability of the four caregiver engagement techniques and construct validity of a Caregiver Engagement factor. Moreover, greater use of caregiver engagement techniques was associated with improved outcomes for adolescent substance use. Counterintuitive results were found suggesting greater use of caregiver engagement techniques exacerbated externalizing symptoms, internalizing symptoms, and family cohesion per youth-report but not caregiver-report. Results of post-hoc analyses indicated therapists may respond to worsening symptom presentation with greater efforts to involve caregivers in treatment. Implications for improving caregiver engagement in youth mental health services more broadly are discussed.