Unlike earthquakes, debris flows can be predicted and avoided to some extent. Earthquakes occur without warning and create most of their destruction within minutes. But rainfall-induced debris flows develop over several hours, leaving some time for forecasting, warning, and emergency response. The USGS and the National Weather Service operated a real-time warning system for rainfall-induced debris flows in the San Francisco Bay region for a decade (1986-1995), and were usually able to provide a general advisory (a watch) early in the storm. When necessary, they provided a warning at the beginning of significant debris flow activity.
Even if a school is in the path of a potential debris flow, there should be time for an orderly evacuation, that is if an advisory is issued, and if an evacuation plan exists. The plan must include enough school buses, drivers, and a system for deciding who goes in which bus. Most important, the plan must include a safe place to take kids until the storm passes and their parents can pick them up.