I wish I knew. Both of my kids show an unusually high amount of tenacity towards mastery... if they are interested. They will obsess and hyper-focus until they have reached a goal. The only downside is that the goal is usually winning some kind of game or perfecting a sport or art skill. Very seldom does their drive apply towards school work.
I suppose I understand. Where is the relevance? If you are six and your older sister will teach you cartwheels when you get home, do you really care about drawing a picture with more than one colour and writing a sentence about it? C'mon!! Cartwheels!!!
I know parents who motivate with money, an idea I've toyed with but never employed. I know others who use discipline to get grades, which I've also never done. My ideal method is inspiration - I just haven't figured out how to do it yet.