I have read a very interesting book about a free school called Summerhill where the children are free to learn and/or play when they want. It's an interesting experiment.
The results that were observed were that during the childhood the children tend to only want to play. Only once they played enough, usually in the teen age, they will start to get bored and want to learn something, and choose to go to class by themselves (class is optional there). When they choose to go to class it is often because they become interested in their future and find the motivation by themselves to learn hard enough, and that compensates the time they have "lost" playing during their childhood.
The good point with that school is that the kids can grow at their own rate without being put under pressure. And somehow it seems to work well, because those people become happy and inspired.
Have a look here:
A. S. Neill's Summerhill School