The National Institute of Justice has released two research reports on investigating the effectiveness of school resource officers (SROs).  You can find them here, or at the links below. 

• Investigator-Initiated Research: The Comprehensive School Safety Initiative Study of Police in Schools. This study assesses the effects of SROs on school disciplinary offenses and actions. The research addresses whether the effects of SROs vary by student characteristics, SRO approach, or school and community characteristics
   
• School Climate, Student Discipline, and the Implementation of School Resource Officers. This study examines the impacts of SROs on outcomes related to school climate and student suspension rates, with a focus on racial differences and the role of school context. This study also examines how SROs perceive their roles and how these may be shaped by school contexts.