This study investigated the effects of a pilot implementation of a trauma supplement intervention, based on the Attachment, Regulation, and Competency (ARC) Model (Blaustein & Kinniburgh, 2019), on Head Start agency attitudes, teacher secondary traumatic stress, classroom climate, and child social-emotional functioning. One hundred and six children, ages 3-4, enrolled in a Head Start preschool in the 2014 school year, their teachers (N= 5), and teacher assistants (N=5) participated. Two half-day trainings on trauma-informed practice based on the ARC framework over a period of six weeks was provided. This was done as a supplement to the social emotional curriculum, Al's Pals (Geller, 1999), already in place (i.e., trauma supplement intervention group, N=3 teachers; N=3 teacher assistants). The comparison site implemented the social-emotional curriculum as usual (i.e., Al's Pals) but did not receive any training on trauma-informed practices (i.e., intervention-as-usual comparison group, N=2 teachers; N=2 teacher assistants). Results of agency-level analyses suggests that while administrators acknowledged the importance of trauma-informed practices, few practices were in place prior to or following the implementation of the intervention. Teachers in the intervention group (N=3) reported positive effects of the intervention on their knowledge regarding trauma informed care. Minimal differences in the domains of positive climate, negative climate, and sensitivity were noted at posttest in classrooms in both the intervention and comparison conditions. Children that had experienced trauma and received the trauma supplement intervention demonstrated marginal improvements in social-emotional functioning. Based on study results, utilizing trauma-informed interventions in school settings must first attend to administration (i.e., agency attitudes) and teacher buy-in. (author abstract)