From Sandra Dodd, on unschooling:
The way adults tend to learn things is the way people best learn—by asking questions, looking things up, trying things out, and getting help when it's needed. That's the way pre-school kids learn too (maybe minus the looking things up), and it is the way "school-age" kids can/should learn as well. Learning is internal. Teachers are lovely assistants at best, and detrimental at worst. "Teaching" is just presentation of material. It doesn't create learning. Finding learning in play is like the sun coming out on a dank, dark day.
And here's a link to her article on playing.