Therapy animals have been frequently included in interventions for children with autism spectrum disorder (ASD); however, direct and systematic procedures such as assessing preference for and reinforcing efficacy of the animals are rarely conducted. Assessing preference for stimuli is valuable when determining how to make interventions for children with ASD most effective. We conducted paired-stimulus preference assessments and follow-up reinforcer assessments to determine if a therapy dog might be an effective reinforcer. We found one third of participants preferred the dog the least, one third of participants moderately preferred the dog, and one third of participants highly preferred the dog relative to other stimuli. Furthermore, we found preference predicted reinforcing efficacy for five of six participants. We suggest clinicians systematically conduct assessments to clearly identify the role of the therapy animal, to improve quality of, and demonstrate efficacy of interventions including animals for clinical populations.