Training Dogs, Training Owners

Well Im half way through my dog trainer/instructor course and it hard. Most people think it really simple but to do it the right way without confusing the animal is crazy. My dog is great she is so easy to train. Teaching others to use the commands is more difficult then I expected. I give them the tools and all they have to do is go home and follow through. They never use the command, then come back to class and say that the dogs not learning. I get tired of hearing 'my dog is dumb' or 'she/he just won't do what I say'. It really drives me nuts. I hope it gets easier but I really doubt it.