The Virginia Student Threat Assessment Guidelines were developed in response to studies of school shootings conducted by the U.S. Federal Bureau of Investigation, U.S. Secret Service, and U.S. Department of Education that recommended schools should adopt a threat assessment approach to prevent targeted violence. This article reviews the development and field-testing of the guidelines in a series of studies, and then describes the challenges of conducting a randomized controlled trial of threat assessment. The design, measurement, and logistical challenges of conducting rigorous research on student threat assessment are discussed. (Published Abstract)