The purpose of this study was to examine the effect of occupational therapy group intervention using Trust Based Relational Intervention® (TBRI®) Nurture Groups© on preschool children's social, emotional, and behavioral development in a Head Start program. This study used a retrospective mixed method, quasi-experimental design with non-equivalent groups and pretest-posttest measures. The intervention site teaching staff participated in 16 hours of TBRI® Caregiver training and the children participated in 12 weeks of Nurture Group© interventions. The Strengths and Difficulties Questionnaire (SDQ) and Teaching Strategies GOLD® (TSG) assessment measured child development in social, emotional, and behavioral domains. The intervention site teaching staff participated in a focus group to determine their perceptions of the intervention's effectiveness. This data was evaluated using grounded theory methodology. SDQ: The children experienced statistically significant changes in the emotional symptoms and prosocial behavior domains. TSG: Results indicated a statistically significant main effect of site on objectives of Forms Relationships with Adults, Responds to Emotional Cues, and Balances Needs & Rights of Self and Others. Themes identified from qualitative analysis illustrated how the teachers highly valued the TBRI® training and adapted their teaching strategies to incorporate the TBRI® principles of empowering, connecting, and correcting. Teaching staff reported increased perceived social-emotional skills in the children and detailed how the children's behavior changed to demonstrate these skills. Occupational therapy group intervention supports the social-emotional development of children attending Head Start. Occupational therapy practitioners need to engage in universal and targeted approaches to promote resiliency in this population of at-risk children.