Abstract Children with acquired brain injuries (ABI) treated on an inpatient rehabilitation unit are at significant risk for long term functional impairment, highlighting the importance of maximizing the effectiveness and utilization of inpatient rehabilitation therapies. The proposed crossover trial seeks to determine the effect of animal-assisted therapy (AAT) during inpatient rehabilitation following pediatric acquired brain injury. To accomplish this objective, we will employ a within subjects cross-over trial. Data will be collected during four therapy sessions across two weeks (2 in week 1 of admission and 2 in week 2 of admission). AAT, via integration of dogs into patient's physical therapy (PT) and occupational therapy (OT) session, will occur during one of the two sessions in the first week and one of the two sessions the second week. The non-AAT condition will be treatment as usual (TAU) as defined by the patient's treatment team, resulting in 2 AAT sessions and 2 TAU sessions total. The order of condition will be randomized separately for each week. We will recruit 90 patients ages 4-21 being treated for ABI on the inpatient rehabilitation unit at CCHMC. We have engaged a highly qualified multidisciplinary team to ensure the safety, feasibility, and effectiveness of the methods. We will accomplish the following aims: 1) determine the effect of AAT on patient engagement in inpatient rehabilitation therapies, 2) examine potential mechanisms of action for AAT-associated improvement in patient engagement (mood and physiological distress), and 3) determine factors that moderate the effect of AAT on patient engagement (patient anthropomorphism, patient-animal closeness, time course in admission, and demographic and injury characteristics). We hypothesize that a greater level of patient engagement will be observed during AAT sessions compared to treatment as usual (TAU) sessions. Additionally, AAT will be associated with more positive mood and lower levels of distress, which in turn will be related to greater patient engagement. Finally, a greater effect of AAT will be noted earlier during patient admissions, and greater levels of anthropomorphism and patient-animal closeness will be associated with greater levels of patient engagement during AAT sessions. We propose the use of novel methodology and innovative technology in data collection designed to address concerns related to bias and reliance of subjective outcomes in the AAT evidence base. This innovation positions the project to fill an important gap in the existing AAT literature. Findings will provide critical new insights into why pediatric inpatients benefit from AAT and who is most likely to benefit. We will translate our findings to ultimately improve functional outcomes following pediatric brain injury, a leading cause of disability.