I've seen teachers make their way to the classroom using the online route, the field practicum route over the course of two years, and also switching careers and using their original degree plus some extra classes to get a teachers license to begin in the classroom. Oh...and who can forget those day care center workers who consider themselves preschool teachers. I hope I don't offend too many people, but I strongly believe that a teacher must be taught how to teach.
A recent panel of very important people met to discuss what is the best teacher preparation programs out there. They found that there is not enough substantial data out there to determine what is the best.
Link here for the full panel report:
Expert Panel Finds No Edge for Traditional vs. Alternative