There has been a growing interest in placing sworn law enforcement officers in schools as School Resource Officers (SROs) as a means of improving school safety and improving relations between police officers and youth. However, when this project began in May 2000, relatively little was known about SRO programs. The purpose of the National Assessment was to identify what program "models" have been implemented, how programs have been implemented, and what lessons they may have for other programs. To obtain this information, Abt Associates and its subcontractors collected implementation data by telephone and on site from 19 SRO programs. This information forms the basis of this case studies report. The report begins with a separate case study of each of the five large established programs. Each case study begins with a capsule description of the program followed by a detailed account of its context, history, and operations. Although all five large established programs serve multiple schools, within four of these five programs the researchers singled out a single school for intensive study based on the recommendation of the program supervisor. As a result, much of the information in these four case studies is based on the experience of a single school. (Contains 6 Appendices.)