**an excerpt from A Novice Looks at Puppy Aptitude Testing, By Melissa Bartlett, originally published in Pure Bred Dogs, American Kennel Gazette, March 1979
1-3 weeks (1-20 days). The puppy needs warmth, food, sleep, and his mother. Neurologically very primitive, the puppy responds by reflex and essentially it is unable to learn.
4th week (21-28 days). The puppy needs its mother most at this time. It is a period of extremely rapid sensory development. Neurologically the brain is suddenly able to receive messages; the circuits are “turned on.” Weaning should NOT take place at this time; the puppy is extremely vulnerable.
5th to 7th week (29-49 days). The puppy needs his mother and litter mates. Dogs removed from the litter at this period tend to be unable to socialize with other dogs, may fight, refuse to breed, etc. Contact with humans and gentle training is beneficial and helps the pup set the stage for more intense contact with humans later on.
7th week (49th-56th day). This is the ideal time for the puppy to transfer his loyalty to his new owner. Mentally he is able to learn whatever any adult dog can learn, his brain is neurologically complete. However, physically he will not be able to do the tasks of an adult dog. For example he can’t jump one and a half times his height with the dumbbell in his mouth, but he can learn the exercise if it is scaled down to his size. Socialization and training should continue on a regular basis. Bonds formed at this time are extremely strong.
8-10 weeks (57-70 days). This is the fear imprinting period. Any traumatic experience such as shipping, ear cropping, severe punishment, etc. may have a lasting effect on the dog. New experiences must be non-fear producing. Proper training and socialization should continue.
11-16 weeks (71-112 days). The puppy continues to learn from his experiences. If left with other dogs, he may become imprinted only to dogs, taking his leadership from them and never developing a strong relationship with human beings. Lack of socialization with humans will result in shy behavior such as found in wild animals. Lack of exposure to other environments and exploration may result in “kennel syndrome,” where the dog is unable to cope with any change from his routine environment.