To find a substitute teacher, many school systems use the Smart Find Express. This is a system that manages employee absences and automatically sends requests to nearby applicable substitute teachers to fill the absence. Alternatively, TheSubService.com or Craigslist are also used at times.
The services available for finding a substitute teacher vary from district to district. If the school system is not set up with Smart Find Express, it may need to network around to see what substitutes other teachers know or have used to get a good idea of who would work best for the class that needs a teacher.