Boxers have a very long puppyhood and adolescence. They are not considered fully mature until age three, one of the longest times in dogdom, and thus need the early training to keep their high energy from wearing the owner out.
Dog Pictures
Afghan Hound
Airedale Terrier
Akita
Beauceron
Bedlington Terrier
Bloodhound
Boston Terrier
Bernese Mountain Dog
Boxer
Corgi
English Spaniel
Griffon
Jack Russell Terrier
Labrador Retriever
Masitff
Newfoundland
Pekingese
Poodle
Tibetan Spaniel