A growing body of knowledge exists about what works for children with mental health needs. There is a paucity of literature to describe the experiences of service providers or service-providing agencies as they work toward implementing evidence-based practices or provide an understanding of their effectiveness in “real-world” settings. No research exists that examines the effectiveness of specific treatment modalities with children with severe emotional disturbance who participate in comprehensive mental health service systems (systems of care). This article describes the experiences that a community mental health agency and an evaluation team had when implementing parent-child interaction therapy, an evidence-based practice, in a system of care.