Show vs.Tell in a Montage

How much should be shown or told in a montage?

 Many stories have a stretch near the middle when the protagonist is in a static state.  There are few ups and downs, and he is often training, learning, journeying, and otherwise preparing for the events to come.  For instance, in the movie Karate Kid, the montage illustrates Daniel's training with Mr. Miyagi.  The montage allows the audience to experience a large stretch of time in only a few minutes.  The viewer understands that when the montage is over, the protagonist now has the skills necessary to fight his "demons". 

In my WIP, my protagonist is about to enter one of these training periods.  I can't figure out how to go about showing the passage of time and giving the reader an idea of what has transpired, without spending too much time on unnecessary details.  How much should I show, and how much should I tell?

Do any of you have experience with this part of their story?  Or can anyone think of a book in which the author did a great job of executing a section this way? 
Now if only life could include a montage.  I would spend my day writing and playing with my kids, followed by a five minute montage in which I do the dishes and the laundry.