This study presents the findings of a quasi-experimental feasibility study examining the Tertiary First Step intervention, an enhanced version of the First Step to Success early intervention program. Tertiary First Step was developed to engage families more effectively and influence and improve parenting practices for children having challenging behavior. Process (fidelity, dosage, and social validity) and outcome data were collected for all participants in the Tertiary First Step condition (N = 33). Parent- and teacher-reported outcomes were collected for the comparison condition (N = 22). Process data suggest the intervention was implemented with fidelity, and that teachers, parents, and coaches perceived the intervention as socially valid. This study presents the first empirical examination of the Tertiary First Step variation. The outcomes provide compelling evidence that the Tertiary First Step intervention is promising for improving student outcomes on social-behavioral indices, decreasing problem behavior, and improving academic engaged time.