Critical periods in your puppies psychological growth:
0 to 7 Weeks - Neonatal, Transition, Awareness, and Canine Socialization
Puppy is with mother and littermates. During this period, puppy learns about social interaction, play, and inhibiting aggression from mother and littermates. Puppies must stay with their mother and littermates during this critical period. Puppies learn the most important lesson in their lives--they learn to accept discipline.
7 to 12 Weeks - Human Socialization Period
The puppy now has the brain waves of an adult dog, but his attention span is short. This period is when the most rapid learning occurs. Learning at this age is permanent so this is a perfect time to start training. Also, this is the ideal time to introduce the puppy to things that will play an important part in his life. Introduce the puppy to different people, places, animals, and sounds in a positive, non-threatening way.
8 to 11 Weeks - Fear Imprint Period
Avoid frightening the puppy during this period. Any traumatic, frightening or painful experience will have a more lasting effect on the puppy than if it occurred at any other time in its life.
13 to 16 Weeks - Seniority Classification Period or The Age of Cutting
Puppy cuts teeth and apron strings! Puppy begins testing who is going to be pack leader. You must discourage any and all biting because such biting is a sign of dominance! It is important that you are a strong and consistent leader. Formal training must begin. Such training will help you establish your leadership.
4 to 8 Months - Play Instinct Period / Flight Instinct Period
Puppy may wander and ignore you. It is very important that you keep the puppy on a leash at this time! The way that you handle the puppy at this time determines if the puppy will come to you when called. At about 4-1/2 months, the puppy loses his milk teeth and gets his adult teeth. That's when puppy begins serious chewing! A dog's teeth don't set in his jaw until between 6 and 10 months. During this time, the puppy has a physical need to exercise his mouth by chewing.
7 to 10 Months - Second Fear Imprint Period / Fear of New Situations Period
Dog again shows fear of new situations and even familiar situations. Dog may be reluctant to approach someone or something new. It is important that you are patient and act very matter of fact in these situations. Never force the dog to face the situation. DO NOT pet the frightened puppy or talk in soothing tones. The puppy will interpret such responses as praise for being frightened. Training will help improve the dog's confidence.
1 to 4 Years - Maturity Period
You may encounter increased aggression and renewed testing for dominance, but because you have spent a lot of time with your dog, this will not present a problem at all - in fact you will probably hardly notice this, it is just something to keep in mind. Continue to train your dog during this period. Your dog may have another fear period between 12 - 16 months of age.