The Office of Special Education Programs (OSEP) in the U.S. Department of Education funded the National Center on Intensive Intervention (NCII, or the Center) in 2011. NCII's mission during the first five years of funding was to build the capacity of local education agencies (LEAs) to support schools, practitioners, and other stakeholders in the implementation of intensive intervention in reading, mathematics, and behavior for students with severe and persistent learning and/or behavioral needs. The purpose of this document is to provide an overview of the Center's accomplishments during the initial funding cycle and to highlight a set of lessons learned from the 26 schools that implemented intensive intervention while receiving technical support from the Center. First, the authors provide a description of NCII's approach to intensive intervention and summarize the Center's initial technical assistance efforts. Next, they describe their methodology and outline the lessons learned from the implementation sites. Then, they offer guidance for practitioners who are interested in implementing intensive intervention. Finally, the authors close with an overview of NCII's plans for building upon this work over the next five years.