Background <p>Despite suggestions that Day Programs can be efficacious, little is understood about which mechanisms create positive change for young people and their family in this setting. The aim of this study was to explore clinician perspectives on how change occurs in an adolescent eating disorder Day Program in Australia.</p> Methods <p>Twelve clinicians working as a team on an adolescent Day Program participated in semi-structured qualitative focus groups. Focus groups explored the clinicians’ perspectives on change processes in the Day Program treatment model and the impact on young people and their families. Data generated from each focus group was analysed using reflexive thematic analysis.</p> Results <p>The structure, predictability and intensity of the Day Program along with tailored and responsive treatment was perceived as leading to a main theme of structural containment. Additionally, the combination of a strong relational treatment focus with team mutuality was perceived as leading to a second main theme of relational containment. The combination of structural and relational containment for families was perceived by clinicians as the leading mechanisms in supporting parental effectiveness in treatment and the settling and engaging of the young people. Levels of containment were also understood to create safety for all (parents, young people, and clinicians) providing a wraparound approach allowing effective treatment to be delivered.</p> Conclusions <p>The findings of this study speak to the importance of safety as a foundation for working with families needing higher levels of care. Treatment approaches that are both structurally and relationally containing might be needed for families requiring more intensive care. Findings also highlight the importance of the clinical team working cohesively and the potential need for clinicians/services to consider how to create a therapeutically supportive environment that maximises the effectiveness of treatment.</p>