In recent years, school districts have converted portions of their bus fleets to cleaner-burning, sometimes cheaper, alternative fossil fuels, such as compressed natural gas or propane. Others have adopted biodiesel, which combines regular diesel with fuel derived from organic sources, usually vegetable oils or animal fats. The number of biodiesel school buses on the road seems likely to grow, but the headline grabbers are two other technologies--all-electric vehicles and hybrids, which employ an electric motor working in tandem with a conventional internal combustion engine. In this article, the author talks about the all-electric vehicles and hybrids and describes how school district fleets are giving road tests to the two technologies.