My feeling is that the real work comes after beginners where we start adding the distraction work and new exercises to stretch their brains even further.
Puppies are no longer puppies by the age of 17 weeks in the eyes of other dogs they have handed in their puppy licence and are now adolescents and as such they have no right to do a lot of the things that puppies can get away with up until this point. This is often when those puppies that have up until that point rushed up to adult dogs and jumped over them, start getting put in their place. Actually it is quite an important thing to allow happen as it will teach them so much quicker than anything we as owners can do. Obviously it has to be a dog that is friendly but that just will not accept bad manners from a young dog and can tell off in a firm but fair way.
The world is a fun place for young dogs and they can easily get distracted by simple things such as smells, leaves or things way off in the distance which cause them not to pay so much attention to you. Like most stroppy teenagers sometimes they will be wonderful and then they turn into Hyde and run off after the dog in the distance or the animal they hear in the wood or do not come in when you call them or down right ignore you when you ask them to do something.
Yes these things can still happen even if you have done your puppy training!
This is where the real work begins and continues during their adolescent life when they are developing the most. You need to teach them that 'even though' there are things that they find interesting they must listen and respect your commands and wait for permission to go and investigate or play.