Citing Gordon Neufeld, author of the 2006 book, Hold On To Your Kids: Why Parents Need to Matter More Than Peers:
"According to the news story, Neufeld says that children between the ages of 4 and 6 aren't ready to learn by working because their brains aren't quite ready for the task. The brain "only gets wired at between 5 and 7 years of age," Neufeld says in the news report.
Play, on the other hand, helps children build problem-solving networks, he says. But that's only if the play is expressive and doesn't have any consequences for making mistakes, or expected outcomes.
Here's the original article by Gordon Neufield: