Different Stages of Development in Puppies

Age (weeks) 3-14. Socialization Period. If socialization later than 14 weeks, (or between 12-14 weeks in some dogs) shyness or aggressiveness may dominate behavior.

Age (weeks) 6-8. Optimum Socialization. If socialization earlier, shyness often develops, alone with over-dependence on owner, which may lead to over protectiveness.

Age (weeks) 8-10. Fear Imprint. Traumatic, fear producing experiences maybe permanently impressed causing defensive reactions in some circumstances.

Age (weeks) 12-14. Puberty Onset. Meaningful sexual mounting often occurs. Males display erections.

Age (weeks) 18-40. Protective-Aggressive. Barking at strangers and other territorial and social group protective tendencies may occur.  Leg lifting may begin in males.

Age (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.

Age (weeks) 104-208. Achievement. Protective -aggressive behavior can become especially purposeful. Problem behavior appears to become self rewarding, habitual. Corrections markedly more difficult.