The National Center on Intensive Intervention (NCII) has a mission to build district and school capacity to implement intensive intervention that will improve reading, mathematics, and behavioral outcomes for students with disabilities in Grades K-12 who have severe and persistent learning and/or behavioral problems. The purpose of this document is to present findings from an exploratory study of how five high-performing districts, which are referred to as NCII's "knowledge development sites," defined and implemented intensive intervention. The findings from this study reflect the most common themes that emerged from the data across all five districts, related to factors that facilitated or created challenges in the implementation of intensive intervention. The findings may offer lessons that other districts can learn from when planning for, implementing, and working to sustain their own initiatives to provide intensive intervention for students with the most severe and persistent learning and/or behavioral needs. The following are appended: (1) Data Collection Materials; and (2) Data Coding Guide.