Facility dogs are trained by canine professionals or by their owner for a period of 18 to 24 months, and must pass very rigorous tests before graduating from an assistance dog organization.[15] In contrast, registration for therapy dogs by a therapy dog organization does not require enrollment in obedience classes or therapy dog classes, meaning that therapy dogs often undergo a much less rigorous training process. Furthermore, the tests that therapy dogs must pass are less complicated and challenging than those taken by facility dogs.[16]