Puppy Development Stages
Weeks 3-14: Socialisation Period. If puppies are socialised later than 14 weeks, (or in some dogs, possibly 12-14 weeks) shyness or aggressiveness may dominate the dog's long term behavior.
Weeks 6-8: Optimum Socialisation. If puppies are socialised earlier, shyness often develops, along with over-dependence on owner, as in separation anxiety, leading to over protectiveness.
Weeks 8-10. Fear Imprint. Fear display experiences maybe permanently impressed causing defensive reactions in some circumstances.
Weeks 12-14: Puberty Onset. Meaningful sexual mounting often occurs. Males display erections.
Weeks 18-40: Protective-Aggressive. Barking at strangers and other territorial and social group protective tendencies may occur. Leg lifting may begin in males.
Weeks 35-56: Functional. Many dogs become more serious about protective-aggressive behavior. A general persistence in behavior problems is noted and corrections become more difficult.
Weeks 104-208: Achievement. Protective, aggressive behavior can become especially purposeful. Problem behavior appears to become self rewarding, habitual. Corrections markedly more difficult.