The purpose of this paper is to describe the implementation of an evidence-based treatment, the Incredible Years® (IY) Small Group Dina Dinosaur Treatment program, as delivered in elementary schools to address the needs of children in kindergarten through second grade with self-regulation difficulties. Adaptations for school-based delivery of 17 intervention groups across three cohorts and 11 schools from an ongoing randomized controlled trial are described and implementation data including qualitative feedback from school stakeholders are presented. Results show that, with implementation supports, this adapted model can be delivered in schools with fidelity comparable to the clinic-based model, although several activities were delivered at lower dosage in the low-income urban schools as compared with low-income rural or better resourced schools. Satisfaction among school counselors, teachers, and parents was consistently high. Implementation challenges include logistics such as space and scheduling, program fit with school practices and policies, use of specific treatment strategies such as time-out within the school context, capacity of school personnel to deliver the program, and selection of students and group composition. Lessons learned can inform adaptation and delivery of other evidence-based clinic treatments in school settings. [This paper was published in "Evidence-Based Practice in Child and Adolescent Mental Health" 2019.]