In my story, the character has to learn a certain skill, with a mentor guiding him. I wrote the introduction and explained some principles regarding the discipline, but I don't want to bore the reader with the practice. And it is necessary that the character improves, in the story.
I want to avoid to do something too abrupt, like "three month later, I was able to...". If it was a movie, it would be a montage!
How can I make that training chapter(s?) more interesting for the reader? Or how can I shorten that?