This study reports on the crash performance of large poststandard school buses (school buses manufactured after April 1, 1977, and weighing more than 10,000 pounds unloaded) in 43 accidents investigated by the National Transportation Safety Board. The report discusses the Safety Board's findings as to how well the standards are working to protect passengers from injury and whether changes in the standards are needed. The study focuses solely on events during the crash: how well the bus performed; how occupants sustained their injuries, if any; and how serious the injuries were. Each school bus passenger's experience in the crash also was analyzed to determine the difference, if any, lap belt use would have made. The report concludes with recommendations to the National Highway Traffic Safety Administration, school bus body manufacturers, and state directors of pupil transportation. Almost two-thirds of the document is devoted to appendices that provide additional data for the analysis. (Author/MLF)