I currently have 4 dogs: 6 year old, 5 year old, almost 3 years old (curly) and then my Great Dane pup.
With the experiences I had, I honestly would say it depends on the dog. Our second to oldest learned everything from our oldest dog. We barely had to house break her, she just watched and followed.
We hope things would be like that for curly but he was so stubborn that he refused to do anything the older two did.
Now with the Great Dane puppy (you may have read my other thread in which curly attacked him), my girl dog, the second to oldest, has taken an interest in training him - she sometimes will bark at him when he is doing something wrong. I don't think the Great Dane is very smart though - or he is just very young because he doesn't seem to get commands as quickly as the other dogs did
Anyhow in short, I really think it depends on the dog...
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