At PetsMart, you can enroll your yorkie in "Puppy Training". They just need to have their first 2 sets of shots and the kennel cough shot (sorry - I don't remember the name of it). This is usually around 12-14 weeks of age.
The cost is $99 for 8/10 sessions. I have found it very helpful...Stomper now knows, sit, lay down, come, don't touch, stay and "do your business". They also teach the dogs how to interact with people/dogs and how to walk by your side. We are in the 4th session and I really feel it is worth the $99!
I will say, that all the other dog owners in the class "baby" Stomper since all the other puppies are 5 times his size. I really don't like that since I don't want him to get "special treatment" and think he can get away with murder!
Good luck!