The purpose of this study was to conduct an experimental analysis of teachers' use of functional assessment (FA) and positive behavior support (PBS) for addressing challenging behaviors in young children. A group of 35 experimental teachers participated in professional development designed to provide step-by-step training and guided implementation of FA linked to PBS intervention planning for children identified with challenging behavior in prekindergarten through first-grade classrooms. A randomly designated group of 35 control teachers received neither training nor consultation for implementing FA and PBS. At post-intervention, experimental teachers reported increased resilience as evidenced in their significantly higher competence and self-efficacy along with greater utilization of FA and PBS practices compared with control teachers. Increased levels of resilience were also documented on multiple measures for experimental children with challenging behaviors who received FA and PBS. Specifically, experimental children demonstrated more positive behaviors and fewer challenging behaviors compared with control children at post-intervention. The findings offer empirical support for providing professional development in FA and PBS as a proactive strategy for promoting improved competence for teachers and, more importantly, for improving resilience among children with behavioral concerns. (Contains 6 tables.)