Research has shown principal support to be a critical variable for implementing and sustaining evidence-based practices. However, there remains little understanding of the factors that may influence a principal's personal decision to support a practice. The purpose of the current study was to examine events that influenced principals' support for a widely-used approach to behavior in schools, school-wide positive behavioral interventions and supports (PBIS). In-depth interviews were conducted with 10 school administrators who self-reported that they were initially opposed to or not supportive of PBIS but became stronger supporters over time. Qualitative analysis using the Enhanced Critical Incident Technique revealed eight helping and three hindering categories of experiences in change in support, as well as two categories of early experiences that they reported might have built their support from the beginning. Implications for enhancing administrator support are provided. [This paper was published in "Journal of Positive Behavior Interventions" (EJ1092466).]