School buses are a difficult issue because they are not in a location long enough to properly monitor for cockroach activity. To locate or pin-point the hot-spots of a German cockroach infestation (live cockroaches, fecal smearing, etc.) on a bus you can use compressed air as a flushing agent under seats, dashboard, door panels, etc.
The bus must be cleaned thoroughly, especially under and in the seats. If possible, vacuum up the cockroaches with a vacuum with a HEPA filter and apply a cockroach bait and growth regulator. Areas to be treated include under the seats, and under the dash where warmth and moisture attract cockroaches.
Find more information about pests in eXtensions Pest Management In and Around Structures Resource Area.