The first textbook on psychology was Principles of Psychology, by Fred Keller and William Schoenfeld. Fred Keller was a friend and colleague of B. F. Skinner and he used an instructional technique known as PSI or personalized System of Instruction. I use this method when I teach my ham radio classes because people progress at different rates, so do animals. I still think it is a good idea to enroll your dog in an obedience class, but the class is not enough. One should work on training the dog throughout it’s life. Stay with it, don’t put unreasonable expectations on the dog and have fun with it.