The safety of America's schools is a major issue. Yet, the magnitude of the problem cannot be accurately assessed because some of the data concerning incidents and disciplinary actions come from reporting systems that are seriously flawed. In this article we examine how data from student self-report surveys and other sources can be used to assess the weaknesses in current school incident-reporting systems and improve the validity of surveillance data on school violence. Particular attention is paid to assessing the validity of data from Gun-Free Schools Act (GFSA) reports on the number of guns in schools in light of nationally representative student survey data. We also discuss the difficulties of obtaining accurate surveillance data and suggest changes in surveillance systems that could produce more valid estimates of violence and injury in our nation's schools. © 2001 John Wiley & Sons, Inc.