I am a great fan of starting as young as possible. When I start to breed with June, I am planning to clicker train the pups before they leave home. They will also be leaving with a clicker and a training instruction booklet.
Anyway, June graduated from her first puppy class at four months! We are enrolling in another one in August, so we have a lot to work on. At 18 weeks, she can sit, lie down, stand on her hind legs, beg, wait and kiss. She also has a great recall. We are working on stay, high five and shake.
She isn't even the smartest puppy, I just started early. Cash is much smarter than she is, but starting early has really given her an advantage. I would recommend it to anyone.
By starting early, you can control them when they reach the difficult teenage stage. I wish I had started earlier with Cash, we started at about 6 months - in the midst of his teenage rebellion. June is almost 5 months now and we are prepared for the terrible teens!